Catalytic Hydrogenolysis of Glycerol to 1-Propanol Using
Bifunctional Catalysts in an Aqueous Media
by
Chau Thi Quynh Mai
A thesis
presented to the University of Waterloo
in fulfillment of the
thesis requirement for the degree of
Doctor of Philosophy
in
Chemical Engineering
Waterloo, Ontario, Canada, 2016
© Chau Thi Quynh Mai
ii
AUTHOR'S DECLARATION
I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including
any required final revisions, as accepted by my examiners.
I understand that my thesis may be made electronically available to the public.
iii
Abstract
Biodiesel is an attractive alternative fuel obtained from renewable resources and glycerol is
produced as a major byproduct in the biodiesel industry. Upgrading glycerol to other valuable
chemicals will contribute to an economic sustainability of the biodiesel industry. Valuable
commodity chemicals such as 1,2-propanediol (1,2-PD), 1,3-Propanediol (1,3-PD) and 1-Propanol
(1-PO) could be produced by catalytic hydrogenolysis. Although much work has been done
towards the conversion of glycerol to 1,2-PD and 1,3-PD, the direct conversion of glycerol to 1-
PO has not received much attention. From an industry point of view, the production of 1-PO is
very interesting. 1-PO has potential applications as a solvent, organic intermediate and can be
dehydrated to produce “green“ propylene for the production of polypropylene. Therefore, the
development of a new process for the efficient conversion of glycerol to 1-PO will contribute to
new “green” chemicals which will benefit the environment and make biodiesel processes more
profitable as 1 kg of glycerol is produced for every 10 kg of biodiesel.
In this research, heterogeneous hydrogenolysis of glycerol to 1-PO was carried out in a batch
reactor using a bi-functional catalyst (prepared by a sequential impregnation method) in water, a
green and inexpensive liquid medium. It was found that a bi-functional solid catalyst consists of a
non-noble metal Ni for hydrogenation and an acidic function of silicotungstic acid (HSiW)
supported on alumina (Al2O3) to be an active catalyst for the one-pot synthesis of 1-PO from
glycerol and H2 in a liquid phase reaction. A systematic study has been carried out to assess the
effects of operating conditions on the glycerol conversion. The catalysts were characterized using
BET, XRD, NH3-TPD, TPR, TGA and FTIR techniques.
The effect of different metals (Cu, Ni, Pd, Pt and Cs) supported 30HSiW/Al2O3 catalyst,
heteroatom substitution (HSiW, HPW and HPMo) on NiHPA/Al2O3 catalysts and 10Ni/30HSiW
supported on different supports (Al2O3, TiO2 and MCM-41) were studied to determine to what
extent these components affect the catalytic activity of the NiHPAs/Al2O3 catalysts for the
hydrogenolysis of glycerol. The effect of the preparation process on the catalytic activity and the
structure of the catalyst was also studied.
It was found that 1%Pt is the best promoter for the production of 1-PO in a stainless steel batch
reactor (the selectivity to 1-PO was 59.2% at 45.3% conversion of glycerol). 1%Ni, a much
iv
cheaper metal, has fairly comparable reactivity to 1%Pt (the selectivity to 1-PO was 54.7% at
39.2% converison of glycerol). It was reported that the catalytic activity and thermal stability
towards decomposition of the catalyst dependends on heteroatom substitution. Using NH3-TPD,
XRD and FTIR it was found that while the Keggin-structure of HSiW and HPW supported catalyst
is stable up to a treatment temperature of 450oC, the Keggin-structure of a HPMo supported
catalyst was decomposed even at a treatment temperature of 350oC; the decomposition of HPMo
into MoO3 is likely to be responsible for the inactivity of the NiHPMo catalyst for glycerol
conversion. HPW and HPMo lost their acidity much more readily than HSiW, and a HSiW
supported catalyst was the best candidate for 1-PO production. The catalytic activity and the
acidity of 10Ni/30HSiW supported catalyst are influenced strongly by supporting 10Ni/30HSiW
on different supports.
Using XRD and FTIR it was found that the thermal treatment during the preparation process indeed
affected the structure and the activity of the catalyst to some extent. The loss in activity of the
catalyst, the decomposition in Keggin-structure of HPAs occur if the treatment temperature is
higher than 450oC.
It is important to note that this is the first report on a 10Ni/30HSiW suported catalyst developed
for the one-pot hydrogenolysis of glycerol in a water media with high conversion of glycerol
(90.1%) and high selectivity to 1-PO (92.9%) at 240oC and 580PSI hydrogen using a Hastelloy
batch reactor. The activation energy Ea of this reaction is 124.1kJ/mol.
Reaction pathways for the hydrogenolysis of glycerol using a bifunctional catalyst
10Ni/30HSiW/Al2O3 is proposed. It is believed that acidity plays an important role for the
dehydration and Ni plays an important role for the hydrogenation. It is suggested that with acidic
catalysts, the main route for the formation of 1-PO from glycerol is via either the hydrogenation
of acrolein or further hydrogenolysis of 1,2-PD (and 1,3PD) where 1,2-PD (and 1,3-PD) and
acrolein are the intermediate species in the formation of 1-PO from glycerol. The formation of 1,2-
PD and 1,3-PD takes place through an initial dehydration of the primary or secondary hydroxyl
groups on glycerol to give acetol or 3- hydroxylpropanaldehyde (3-HPA). The hydrogen activated
on the metal facilitates the hydrogenation of acetol or 3-HPA to release 1,2-PD or 1,3-PD
respectively. However, dehydration of 3-HPA on the acid sites forms acrolein. Further
hydrogenolysis of diols or hydrogenation of acrolein produces 1-PO.
v
1,3-PD that is a very high value-added chemical can also be obtained from hydrogenolysis of
glycerol using a Ni-HSiW supported catalyst. To improve the selectivity of 1,3-PD it is suggested
that the catalyst should have high hydrogenation activity for the intermediate 3-HPA. The
equilibrium between acrolein and 3-HPA in the hydration-dehydration step is important, so it is
essential to tune the bi-functional catalyst and the conditions of the reaction to form 1,3-PD from
3-HPA. A study of promoter effects for the activity of catalyst to form 1,3-PD is recommended.
vi
Acknowledgements
To achieve the Ph.D degree is my first important objective since I came to Canada. I was lucky to
get the chance to accomplish my wish at the University of Waterloo. The Ph.D program is
challenging both academically and personally. I appreciate the encouragement, support,
instruction, tutorial, and cooperation provided by the Department of Chemical Engineering and
the University of Waterloo during the past five years. Without this help, my study in pursuing this
degree would have been much more difficult.
First of all, I would like to express my sincere gratitude to my supervisor, Professor Flora T.T. Ng
for her academic instruction, research guidance, continuous encouragement, financial support and
inspiration through the course of this research project. Her professional experience, active research
attitude, and her keen judgement on the study direction are the guiding light in my study. Under
her supervisor my research skills have improved to a higher level. I would also show my gratitude
to Professor Garry Rempel who gives me the chance to extend my knowledge in catalysis, the
helpful discussions and suggestions, and his professional experience.
Secondly, I would extend my gratitude to the committee members in my Comprehensive
Examination and the Oral Defence, Professor Bill Anderson, Professor Aiping Yu, Professor
Zhongchao Tan, and Professor Ying Zheng for their constructive comments and contributions to
this thesis. I would also show my gratitude to the lecturers of the four courses I took during my
Ph.D program. They are Professor Garry Rempel, Professor Thomas A. Duever, Professor
Zhongwei Chen and Professor Michael K.C. Tam. The study on these courses was very helpful in
completing this thesis.
I would like to thank all the members of Professor Ng’s research group during my study. Special
thanks to Dr. Yuanqing Liu for helping me start the experiments with the autoclave, GC and
catalyst preparation techniques. Thanks to Dr Guo - a visiting professor from China for helping
me with the DRIFT and TPD techniques, and for sharing his valuable experience and knowledge.
Thanks to Dr. Nagaraju Pasupulety for helping me with the TPD and XRD experiments. Thanks
to Dr. Lei Jia for helping me with the RGA and TEM experiments. Thanks to all other members
for their help with my experiments and their friendship: Ashish Gaurav, Lu Dong, Saurabh
Patankar, Manish Tiwari. Thanks to the undergraduate students who helped to get the excellent
vii
data: Aprajita Bansal, Beatrize Vieira, Hsin-Ya Lo, Gurjant Singh Sidhu, Eghosa Ogbeifun and
Arnaud N. Gatera. Thanks to the members in Professor Rempel’s group for their helping with the
equipment: Dr. Allen Liu and Dr Karl Liu. I would acknowledge the kind assistance of Ralph
Dickhout, Bert Habicher, Ravindra Singh and Rick Hecktus during my research.
As a daughter, I would like to bow my deep gratitude and my love to my parents, Cu Mai and
Dong Phan. I appreciate them raising me up, providing me a comfortable growing up environment,
supporting my education, and giving me their great selfless love. I would like to send my
appreciation to my siblings, Phuong Mai and Khoa Mai, who supported and took care of my
parents all the time during my study.
Finally, I want to express my deep gratitude to my husband, Hai Le, for his constant
encouragement, understanding, and support throughout my study and my life. I also appreciate the
birth of my sons, Son Le and Daniel Le, who gave me a lot of happiness during my study.
The financial support from the Natural Sciences and Engineering Research Council (NSERC) of
Canada, Vietnam International Education Development (VIED) and PetroVietnam of Vietnam is
gratefully appreciated.
viii
Table of Contents
Abstract .......................................................................................................................................... iii
Acknowledgements ........................................................................................................................ vi
Table of Contents ......................................................................................................................... viii
List of Figures ................................................................................................................................ xi
List of Tables ................................................................................................................................ xv
Nomenclature .............................................................................................................................. xvii
Chapter One .................................................................................................................................... 1
General of Background ................................................................................................................... 1
1.1 Introduction ........................................................................................................................... 1
1.2 Glycerol production and markets .......................................................................................... 2
1.3 Glycerol as a platform chemical............................................................................................ 4
1.4 Converting glycerol into value-added products .................................................................... 5
1.5 Uses of 1,2-Propanediol, 1,3- Propanediol and 1-Propanol .................................................. 8
1.5.1 1,2-Propanediol............................................................................................................... 8
1.5.2 1,3-Propanediol............................................................................................................... 8
1.5.3 1-Propanol ...................................................................................................................... 9
1.6 Research objective............................................................................................................... 10
Chapter Two.................................................................................................................................. 12
Literature Review.......................................................................................................................... 12
2.1 Introduction ......................................................................................................................... 12
2.2 Reaction mechanism for the heterogeneous hydrogenolysis of glycerol to lower alcohols 12
2.3 Heteropolyacids ................................................................................................................... 18
2.4 Catalyst for production of 1,3-Propanediol from glycerol .................................................. 20
2.4.1 Promoting effect of Tungsten-added catalysts in the generation of BrØnsted acid ..... 20
2.4.2 Noble metal based catalysts .......................................................................................... 22
2.5 Catalysts for production of 1-Propanol from glycerol ........................................................ 25
Chapter Three................................................................................................................................ 27
Experimental Apparatus and Methods .......................................................................................... 27
3.1 Materials .............................................................................................................................. 27
ix
3.2 Catalyst Preparation Methods ............................................................................................. 27
3.2.1 The preparation of metal heteropolyacids supported catalyst by impregnation ........... 27
3.2.2 Loading Cs on 10Ni/30HSiW/Al2O3 catalysts by ion-exchanged method................... 28
3.3 Autoclave Experimental Apparatus .................................................................................... 28
3.3.1 Catalyst reduction apparatus ......................................................................................... 28
3.3.2 Autoclave apparatus ..................................................................................................... 29
3.4 Products Analytical Apparatus and Method ....................................................................... 30
3.4.1 Gas Chromatography (GC) ........................................................................................... 30
3.5 Methods and Procedures for Catalyst Characterization Techniques ................................... 33
3.5.1 AmmoniaTemperature Programmed Desorption (NH3-TPD) ...................................... 34
3.5.2 H2 Temperature Programmed Reduction (TPR) .......................................................... 36
3.5.3 Brunauer Emmett Teller (BET) Surface Area .............................................................. 36
3.5.4 Thermal Gravimetric Analysis (TGA) ......................................................................... 38
3.5.5 X-Ray Diffraction (XRD) ............................................................................................. 38
3.5.6 Fourier transform infrared spectroscopy (FTIR) .......................................................... 39
Chapter Four ................................................................................................................................. 40
Conversion of glycerol to lower alcohols using 10Ni/30HSiW/Al2O3 catalyst in a Stainless Steel
batch reactor .................................................................................................................................. 40
4.1. Effect of metals on the hydrogenolysis of glycerol............................................................ 40
4.2 Effect of Cs+ on activity of 10Ni/30HSiW/Al2O3 catalyst .................................................. 48
4.3 Conclusions ......................................................................................................................... 61
Chapter Five .................................................................................................................................. 63
Conversion of glycerol to lower alcohols using 10Ni/30HSiW/Al2O3 catalyst in a Hastelloy
reactor ........................................................................................................................................... 63
5.1 Repeatability of 10Ni/30HSiW/Al2O3 Catalyst .................................................................. 63
5.2 Effect of experimental parameters ...................................................................................... 64
5.2.1 Effect of RPM ............................................................................................................... 64
5.2.2 Effect of hydrogen pressure .......................................................................................... 69
5.2.3 Effect of water content ................................................................................................. 75
5.2.4 Effect of catalyst weight loading .................................................................................. 79
5.2.5 Kinetic analysis............................................................................................................. 81
x
5.2.6 Effect of temperature and activation energy ................................................................. 83
5.3 Study of the effect of NiHSiW/Al2O3 loading on Al2O3 ..................................................... 88
5.3.1 Effect of HSiW loading on catalytic activity of the 10Ni/HSiW/Al2O3 ....................... 88
5.3.2 Effect of different amounts Ni loading ......................................................................... 95
5.3.3 Effect of catalyst preparation sequence on 10Ni/30HSiW/Al2O3 catalysts ............... 102
5.4 Proposed reaction mechanism using heterogeneous metal catalysts ................................ 108
5.5 Leaching and recyclability of catalyst ............................................................................... 113
5.6 Conclusions ....................................................................................................................... 115
Chapter Six.................................................................................................................................. 117
Keggin type Heteropolyacid supported catalyst for hydrogenolysis of glycerol to 1-Propanol . 117
6.1 Efficient hydrogenolysis catalysts based on Keggin polyoxometalates............................ 117
6.2 The effect of thermal treatment on activity and structure of 10Ni/30HSiW/Al2O3 catalyst
................................................................................................................................................. 126
6.3 Effect of different supports on activity of 10Ni/30HSiW supported catalyst ................... 143
6.4 Conclusion ......................................................................................................................... 152
Chapter Seven ............................................................................................................................. 153
Conclusion and Recommendation .............................................................................................. 153
7.1 Conclusions on glycerol hydrogenolysis to 1-PO using 10Ni/30HSiW supported catalyst
................................................................................................................................................. 153
7.2 Proposed reaction pathway................................................................................................ 155
7.3 Recommendations ............................................................................................................. 157
References ................................................................................................................................... 159
Appendix A Literature Data........................................................................................................ 177
Appendix B GC Calibration Curve ............................................................................................. 185
Appendix C Acid concentration calculation (mmol/gcat) ............................................................ 191
Appendix D Glycerol conversion, product selectivity and rate constant calculations ............... 194
Appendix E Data of hydrogenolysis of Glycerol (some typical experiments) ........................... 198
Appendix F Permission to Re-print Copyrighted Material ......................................................... 202
xi
List of Figures
Figure 1-1 Global and United State crude glycerol production 2003–2023…………….………...4
Figure 1-2 Processes of catalytic conversion of glycerol into useful chemicals………………….6
Figure 1-3 Market Value of Different Value-added Products from Glycerol in 2016..........……..7
Figure 2-1 Crystal structure of a typical Keggin-type heteropolyanion........................................19
Figure 2-2 Models proposed for the states of acidic protons and water in solid H3PW12O40 …...19
Figure 3-1 Diagram of the Catalyst Reduction Apparatus.............................................................29
Figure 3-2 An Autoclave Reactor System.....................................................................................29
Figure 3-3 A typical chromatogram of a GC calibration standard................................................32
Figure 3-4 Diagram of the Altamira AMI-200 Catalyst Characterization System………....……35
Figure 4-1 XRD patterns of 1 wt% metal loading on HSiW/Al2O3 catalyst….….………...……42
Figure 4-2 XRD patterns of 1wt% and 10 wt% Ni loading on HSiW/Al2O3 catalyst…………...42
Figure 4-3 NH3-TPD patterns of different metals loading on 30HSiW/Al2O3 catalyst………….43
Figure 4-4 NH3-TPD patterns of 1 wt % and 10 wt% Ni supported 30HSiW/Al2O3 catalyst...…43
Figure 4-5 Pseudo-first-order rate constants for the 10Ni/30HSiW/Al2O3 catalysts using different
starting material.….…….……………….……………….……….……….…………...…….…..47
Figure 4-6 NH3-TPD patterns for different Cs+ exchanged……….…………..……….…….…..54
Figure 4-7 Effect of different Cs+ content on acidity of catalyst….………...………..………….54
Figure 4-8 FT-IR spectra of 10Ni/30CsxH4-xSiW/Al2O3…..………………………..………..….55
Figure 4-9 XRD patterns for the 10Ni30CsxH4-xSiW/Al2O3 catalysts with different Cs+ content56
Figure 4-10 Effect of Cs+ on Glycerol Hydrogenolysis and products selectivity as a function of
time................................................................................................................................................59
Figure 5-1 Concentration profiles of different products using 10Ni/30HSiW/Al2O3 catalyst
reduced at 350oC……………………………………………………….……...…………………66
Figure 5-2 Concentration profiles of acetol, 12-PD and Acr using 10Ni/30HSiW/Al2O3 catalyst
reduced at 350oC……………..…………………………………………………………………..66
Figure 5-3 Pseudo-First-Order kinetics analyses in the presence 10Ni/30HSiW/Al2O3 catalysts at
different agigator spead………………………………………………………..…………………68
xii
Figure 5-4 Effect of H2 pressure on glycerol hydrogenolysis and products selectivity as a
function of time…………………………………………………………………..………………72
Figure 5-5 Pseudo-First-Order kinetics plots of H2 pressure effect on hydrogenolysis of glycerol
in the presence of 10Ni/30HSiW/Al2O3 catalyst…………………...............................................74
Figure 5-6 Effect of water content on Glycerol Hydrogenolysis and product distribution...........76
Figure 5-7 Pseudo-First-Order kinetics plots of effect of glycerol feed concentration on
hydrogenolysis of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst…………..……….78
Figure 5-8 Effect of catalyst weight loading on Glycerol Hydrogenolysis and product distribution
.......................................................................................................................................................80
Figure 5-9 Pseudo-First-Order kinetics plots of effect of catalyst weight loading on
hydrogenolysis of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst…………..…..…...80
Figure 5-10 Effect of temperature on glycerol hydrogenolysis and products selectivity as a
function of time…………………………………………………………………………………..86
Figure 5-11 Pseudo-First-Order kinetics analyses for the 10Ni/30HSiW/Al2O3 catalysts at
different temperature .....................................................................................................................87
Figure 5-12 Calculation of the activation energy based on ln(k) and 1/T using the equation
lnk=lnA-Ea/R(1/T) …………………………………..…………………………...…………..….87
Figure 5-13 Effect of HSiW loading on Glycerol Hydrogenolysis and products selectivity as a
function of time .............................................................................................................................91
Figure 5-14 Pseudo-First-Order kinetics plots of effect of HSiW loading on hydrogenolysis of
glycerol in the presence of 10Ni/HSiW/Al2O3 catalyst……………………..…….....…………..91
Figure 5-15 NH3-TPD patterns of different HSiW loading….…………………..……….……...92
Figure 5-16 Effect of HSiW loading on acidity of the catalyst………………….....……..……..93
Figure 5-17 XRD patterns for different HSiW loading………………………..……..……….…95
Figure 5-18 Effect of Ni loading on Glycerol Hydrogenolysis and products selectivity……..…97
Figure 5-19 Effect of Ni loading on glycerol hydrogenolysis and products selectivity as a
function of time………………………………….………………………...…………….….……98
Figure 5-20 Pseudo-First-Order kinetics plots of effect of Ni loading on hydrogenolysis of
glycerol in the presence of Ni/30HSiW/Al2O3 catalyst…………………………………...……..99
Figure 5-21 NH3-TPD patterns for Ni loading…………………………….………….…..……..99
xiii
Figure 5-22 XRD patterns for different Ni loading catalyst........................................................101
Figure 5-23 Effect of preparation sequence loading active components on glycerol
hydrogenolysis and products selectivity as a fuction of time......................................................104
Figure 5-24 Pseudo-First-Order kinetics plots of effect of sequence adding components on
hydrogenolysis of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst......……...………104
Figure 5-25 NH3-TPD patterns for method preparation……….………………....…………….106
Figure 5-26 XRD patterns for method preparation……………………………….…………….106
Figure 5-27 TPR patterns for sequence loading of component……….…………….………….107
Figure 5-28 Hydrogenolysis of glycerol and lower alcohols.......................................................108
Figure 6-1 Concentration profiles of different HPAs supported 10Ni/Al2O3 catalyst at different
reduction temperature at 350 and 450oC…………………….................................................….120
Figure 6-2 Pseudo-First-Order kinetics plots of effect of HPAs on hydrogenolysis of glycerol in
the presence of 10Ni/30HPA/Al2O3 catalyst………...................................................................121
Figure 6-3 NH3-TPD patterns for different HPAs reduced at 350 and 450oC……….....………122
Figure 6-4 Total acidity amount for different HPAs reduced at 350 and 450oC……..………...122
Figure 6-5 XRD patterns for different HPAs calcined at 350oC………………………..……...125
Figure 6-6 FTIR patterns for different HPAs calcined at 350oC…………………………..…...125
Figure 6-7 Effect of calcination temperature on the conversion of glycerol and the distribution to
products as a function of time ………………………………………………………………….130
Figure 6-8 NH3-TPD patterns for catalyst calcined at different temperature…………..………132
Figure 6-9 TPR patterns for catalyst calcined at different temperature………………………...134
Figure 6-10 XRD signal for catalyst calcined at different temperature………………………...134
Figure 6-11 FTIR signal for catalyst calcined at different temperature………………..……….135
Figure 6-12 Effect of reduction temperature on the conversion of glycerol and the distribution to
products as a function of time………………..............................................................................139
Figure 6-13 Pseudo-First-Order kinetics plots for 10Ni/30HSiW/Al2O3 Catalyst reduced at
different temperature…………………………….……………………..……………………….140
Figure 6-14 NH3-TPD patterns for catalyst reduced at different temperature………...…..……141
xiv
Figure 6-15 Effect of supports reduced at 350oC on the conversion of glycerol and the
distribution to products as a function of time…..........................................................................146
Figure 6-16 Effect of supports reduced at 450oC on the conversion of glycerol and the
distribution to products as a function of time..........................................................................…147
Figure 6-17 Effect of supports on Glycerol Hydrogenolysis and products selectivity…………147
Figure 6-18 Pseudo-First-Order kinetic analysis of effect of support on hydrogenolysis of
glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst...............................................………148
Figure 6-19 NH3-TPD patterns for different support. ……..………………...………..………..149
Figure 6-20 Effect of supports on total acidity and acid strength of catalyst reduced at 450oC..150
Figure 6-21 Effect of acidity of catalyst on glycerol conversion and selectivity of products….150
Figure 6-22 XRD patterns for different support……………….………….……………………151
xv
List of Tables
Table 1-1 Physical properties of pure glycerol………………………..………..…………………3
Table 3-1 Detailed GC Method......................................................................................................31
Table 3-2 Retention Time and Response Factor for Each Compound…………...……………...32
Table 4-1 Total acidity of catalysts………………………………………………………………43
Table 4-2 Effect of metal loading on catalytic performance…………………………...………..46
Table 4-3 The hydrogenolysis of 1,2-PD, 1,3-PD and 1-PO……………………………...……..47
Table 4-4 Surface area and total acidity of 10Ni/30CsxH4-xSiW/Al2O3 catalyst………………...54
Table 4-5 Effect of Cs+ on catalytic performance in the hydrogenolysis of Glycerol…………...57
Table 4-6 Effect of Cs+ on catalytic performance of 30HSiW/Al2O3 catalyst in the
Hydrogenolysis of Glycerol…………………………………………………………………...…60
Table 5-1 Repeatability study on 10Ni/30HSiW/Al2O3 catalyst…..………………….…………64
Table 5-2 Effect of agitator speed on the reaction rate and the distribution to products in the
hydrogenolysis of Glycerol…………………………………………………..………………..…65
Table 5-3 Effect of hydrogen pressure on the conversion of glycerol and the distribution to
products in the hydrogenolysis of glycerol……………………………………………………....70
Table 5-4 Effect of water content on the conversion of glycerol and the distribution to products
in the hydrogenolysis of Glycerol…………………...…………………………………………...75
Table 5-5 Effect of catalyst weight loading on the conversion of glycerol and the distribution to
products in the hydrogenolysis of Glycerol…………………..…………….……………………79
Table 5-6 Effect of temperature on the conversion of glycerol and the distribution to products in
the hydrogenolysis of glycerol…………………………………………………….…….…….....85
Table 5-7 Effect of temperature on the reaction rate of hydrogenolysis of glycerol……….……86
Table 5-8 Effect of HSiW loading on the conversion of glycerol and the distribution to products
in the hydrogenolysis of Glycerol using 10Ni/Al2O3……………………………………...…….89
Table 5-9 BET surface area and total acidity of different HSiW loading catalysts……...……....94
Table 5-10 Effect of Ni loading on catalytic activity of the Ni/30HSiW/Al2O3………...……....96
Table 5-11 BET surface are and acidities of different Ni loading catalysts………………..…..100
xvi
Table 5-12 Effect of different sequence loading active components on product distribution….103
Table 5-13 Total acidity of different sequence HSiW loading catalysts……………………….105
Table 5-14 Hydrogenolysis of different starting materials using 10Ni/30HSiW/Al2O3 catalyst109
Table 5-15 Continuing reaction without using 10Ni/30HSiW/Al2O3 catalyst…………...….…...113
Table 5-16 10Ni/30HSiW/Al2O3 catalyst recycling study………………………………..….…114
Table 6-1 Effect of different HPAs supported 10Ni/Al2O3 catalyst on the conversion of glycerol
and the distribution to products in the hydrogenolysis of glycerol……………………………..119
Table 6-2 Effect of different HPAs supported 10Ni/Al2O3 catalyst and reduction temperature on
acidity and catalyst performance……………………………………………………..………...123
Table 6-3 Effect of calcination temperature on the conversion of glycerol and the distribution to
products in the hydrogenolysis of Glycerol……………………………………………….……129
Table 6-4 Effect of calcination temparature on acidity of 10Ni/30HSiW/Al2O3 catalyst……...132
Table 6-5 Effect of reduction temperature on the conversion of glycerol and the distribution to
products in the hydrogenolysis of Glycerol………………………………………………….…138
Table 6-6 Effect of reduced temparature on acidity of 10Ni/30HSiW/Al2O3 catalyst…….…...142
Table 6-7 Effect of support on the conversion of glycerol and the distribution to products in the
hydrogenolysis of Glycerol……………………………………………………………………..145
Table 6-8 Surface area and acidities of 10Ni/30HSiW supported catalysts……………………149
xvii
Nomenclature
1,2-PD = 1,2-propanediol
1,3-PD = 1,3-propanediol
1-PO = 1-propanol
3-HPA= 3-Hydroxypropionaldehyde
Acr = Acrolein
BET = Brunauer–Emmett–Teller
EG = Ethylene Glycol
FID = Flame Ionization Detector
FTIR = Fourier Transform Infrared Spectroscopy
GC = Gas Chromatography
GHG = Greenhouse Gas
HPAs = Heteropolyacids
HPMo = Phosphomolybdic acid
HPW= Phosphotungstic acid
HSiW = Silicotungstic acid
IMP = Impregnation
LD50 = Lethal Dose 50%
LDLO = Lethal Dose Low
PTFE = Polytetrafluoroethylene
RPM = Round per Minute
TCD = Thermal Conductive Detector
TGA = Thermal Gravimetric Analysis
TPD = Temperature Programmed Desorption
TPR = Temperature Programmed Reduction
wt% = weight percent
XRD = X-Ray Diffraction
1
Chapter One
General of Background
1.1 Introduction
Fossil oil is still the main source not only for energy but also for most of the chemical products
used by modern society, including plastics, rubber, perfumes, and pharmaceuticals. Energy is
essential not only in the industrial sector but also important over all aspects of society. The
chemical industry is a cornerstone of human development that influences all aspects of modern
society.
As a source of energy, fossil fuel is non-renewable, produces the pollutants that causes huge
environmental issues and it is not easy to solve. It is important to use other alternative resources
effectively, bring down the reliance on fossil feedstocks and the environmental influence of the
production methods and products [1-3]. The foreseen depletion of petroleum together with an
increased public concern on environmental issues and global climate change has increased the
interest in the replacement of fossil-based chemicals by biomass-based chemicals [4]. It has
motivated many researchers to focus on the conversion of fossil fuels to alternative sources of
renewable energy and shift the petroleum-based society to green, environmentally friendly society.
In view of the fossil-based issues, the idea of green chemistry was developed [5]: ‘‘the chemical
industry needs to be designed in the way that can minimize or eliminate the utilization and
generation of polluted and toxic substances”. In addition, the use of catalysts, which are selective
and recyclable, is one of the important principles of green chemistry.
Several substantial actions can be applied to utilize and modify renewable sources that could have
an enormous influence on human activities. Such implementation can exist in different industries
such as energy, polymer, textile, pharmaceutical, paints and coatings, food etc [4]. Essentially,
they have given rise to a key research area for the replacement of fossil-based raw materials by
biomass. Recently glycerol has emerged as a potential alternative to fossil-based raw materials
and “glycerochemistry” [6, 7] has become an important developing sector that comprises replacing
petroleum-based resources with glycerol as a bio feedstock in the chemical, solvent and fuel
2
industries [8]. Glycerol, also called 1, 2, 3-propanetriol, is a simple sugar alcohol with three
hydroxyl groups. Generally, Glycerol can be obtained either as a by-product from fermentation or
as a by-product in biodiesel production. Glycerol is considered by the US Department of Energy
as one of the 12 building block chemicals obtained from biomass that can be utilized to produce
other high value biomass-based chemicals [9]. Glycerol could be used to produce many valuable
products via oxidation, esterification, hydrogenolysis and others [6]. Upgrading the value of
glycerol will reduce the cost of biodiesel production and help the biodiesel industry.
For a successful bio-based economy, development of biomass-based chemicals and green catalyst
will be important in order to convert to a limited number of building blocks to a range of secondary
products for different applications [10, 1]. In the context of this thesis, glycerol was used as raw
material for C3 platform chemicals such as 1,2-PD, 1,3-PD and 1-PO.
1.2 Glycerol production and markets
Glycerol is a three carbon polyol which is hygroscopic, colorless, odorless viscous liquid under
atmospheric condition. It is sweet tasting in its pure form and low toxicity. Glycerol finds a range
of applications in industry and commerce such as: food industries, pharmaceuticals, personal cares,
plasticizers, tobacco, emulsifiers, antifreeze and so on. It is also a very important raw material to
produce many other chemicals [11]. Some physical characteristics of this compound are listed in
Table 1-1.
Glycerol that is currently available on the market can be obtained by the chemical conversion of
propylene (synthetic glycerol - 10% of the market) or from oleochemical industry especially as a
main by-product in biodiesel production (bio-glycerol - 90 % of the market) [11, 12]. Biodiesel is
produced from renewable sources, together with its biodegradability and non-toxic nature has
become one of the most promising fuels for the future. The major co-product of this process is a
glycerol. For every 9 kg of biodiesel produced approximately 1 kg of glycerol is produced as a
byproduct [13]. A recent surge in the production of biodiesel has created a glut in the glycerol
market. As a result, the value of both crude and refined glycerol has in general decreased over the
years. Dow Chemical in Freeport Texas in the only supplier of synthetic glycerol in the US.
However, the flood of biodiesel-derived glycerol causes this plan to close in January 2006 [14].
3
Table 1-1 Physical properties of pure glycerol [11]
Chemical Structure
Chemical Formula C3H8O3
Molecular Mass 92.09 g·mol-1
Density (at 20 °C) 1.261 g·cm-3
Caloric Value 18 kJ·g-1
Melting Point 18.0 °C
Boiling Point (at 101.9 kPa) 290.0 °C
Electrical Conductivity (at 20 °C) 0.1 μS·cm-1
Fig. 1-1 shows a forecast of the crude glycerol production from the biodiesel industry in the United
States and other countries in the last ten years and for the next ten years. A fast increase of glycerol
production results in a saturation of the market causing prices of crude glycerol and refined
glycerol to drop. The price of refined glycerol varied from $0.2 to $0.7/kg and crude glycerol from
$0.04/kg to $0.33/kg over the past few years in the global market [15]. A flood in the glycerol
market has established [16].
It has been proposed that once the glycerol price drops below US$ 0.23 per kg it would open up
the possibility of using glycerol as a biorefinery feedstock chemical [17]. Prior to the large scale
production of biodiesel, the use of glycerol from biodiesel for this purpose was rarely investigated.
However, as a large amount of crude glycerol is formed in biodiesel plants followed by a drop in
the price of crude glycerol makes glycerol a valuable by-product which could be purified and sold
to increase the profitability of the overrall process [18].
4
Figure 1-1 Global and United State crude glycerol production 2003–2023 [7]*
*Reprinted from Ye X. P. et al., ACS Symposium Series; American Chemical Society: Washington, DC, 2014, Chapter 3, pp. 43–
80 with permission from ACS Publications
1.3 Glycerol as a platform chemical
Platform chemicals are substances with functional groups and are used as building blocks that can
be converted to a wide range of chemicals or materials. Bio-based platform chemicals that are
biodegradable provide a great opportunity for decarbonising everyday products and makes society
more environmentally friendly [19]. Production and conversion of bio-derived platform chemicals
is a very promising approach to provide a sustainable market and reduction of biofuel production
cost [1, 20]. Glycerol is a polyol molecule rich in functionalities, unique structure, biocompatibility
and biodegradability [21] which could become one of the most important platform chemicals for
the biobased chemical industry [19]. Glycerol is considered by the US Department of Energy as
one of the 12 building block chemicals obtained from biomass that can be utilized to produce other
high value biomass-based chemicals [9].
These days, due to government policies to encourage the utilization of renewable resources and to
fulfill the rising energy demand, biodiesel production has rapidly increased. The expansion of
biodiesel production makes glycerol readily available and in large supply. The conversion of
glycerol into other chemicals creates new opportunities for utilizing glycerol as the crude material
[17]. Furthermore sustaining a good price for glycerol can boost other industries like biodiesel
5
which is struggling to gain a foothold. As a result upgrading the value of glycerol will reduce the
cost of biodiesel production and help the biodiesel industry. Significant research has been focused
recently on its conversion to value-added chemicals as a bio platform chemical to replace
mainstream petroleum derived chemicals [17, 21, 22]. There are several chemicals which can be
obtained from the hydrogenolysis of glycerol that have higher value than glycerol such as 1,2-
propanediol (1,2-PD), 1,3-propanediol (1,3-PD) and 1-propanol (1-PO).
1.4 Converting glycerol into value-added products
Utilization of glycerol derived from the growing biodiesel industry is important to oleochemical
industries [23]. In the past, the high value of glycerol made it economically unattractive as a
feedstock chemical and the improvement of alternative processes for glycerol utilization is not
properly considered [16]. Recently, an increase in glycerol supply and a drop in the price of crude
glycerol make glycerol an important building block for the production of a variety of bio-based
chemicals. Biodiesel, designated to be a future alternative fuel, produces crude glycerol as a waste
byproduct. The conversion of this crude glycerol to value added products is a sustainable approach
compared to petroleum-based products. Besides, upgrading of crude glycerol to value added
products affects a substantial effect on the economy of the biodiesel sector. Over the past decades
significant research efforts have been focused on the conversion of glycerol as a low-cost feedstock
to other valuable chemicals and products. Because of the high functionality of glycerol (two
primary and one secondary hydroxyl group), reactions can proceed along multiple reaction
pathways to give mixtures of products. Several good review articles on glycerol conversion to
value-added chemicals and products have been published. In 2008 Zhou C. H. et al. showed from
a technical standpoint several different reaction pathways to produce other chemicals from
glycerol (Fig. 1-2) [24].
In 2008 Pagliaro et al., recapped 22 different possible approaches that can be used to obtain
different valuable products from glycerol and their industrial applications [25]. In 2015 Bagheri
et. al. reviewed and highlighed many possible processes for the catalytic conversion of glycerol
into useful chemicals [6]. Various reactions that are available to derive value added chemicals of
commercial interest from glycerol such as hydrogenolysis of glycerol to propanediols, dehydration
of glycerol into acrolein, steam reforming of glycerol to produce hydrogen were reported
6
[16,24,26,27]. Among the approaches hydrogenolysis of glycerol into lower alcohols have been
reported as promising processes and can produce higher value products such as 1,2-propanediol
Figure 1-2 Processes of catalytic conversion of glycerol into useful chemicals [24]*
*Reprinted from Zhou C.H. et al., Chemical Society Reviews, 2008, 37, pp. 527–549 with permission from the Royal Society of
Chemistry
7
(1,2-PD), 1,3-propanediol (1,3-PD), and 1-propanol (1-PO). 1,2-PD is used primarily for
commodity chemicals and is a green replacement for the toxic ethylene glycol for deicing aircraft.
1,3-PD is a valuable intermediate for the production of high value polymers such as polyester and
polyurethane resins. 1-PO is useful as a solvent, organic intermediate and could be dehydrated to
produce “green“ propylene for the production of polypropylene. The market value of these
chemicals is shown in Fig. 1-3 [28a].
It is clear that 1,3-PD is the most valuable product among these alcohols, followed by 1-PO and
1,2-PD. Thus far, the most effective way to produce 1,3-PD is through fermentation [28b];
however, the low metabolic efficiency and poor compatibility with existing chemical plants make
it less favorable. In recent year the glycerol hydrogenolysis of glycerol to 1,3-PD has been
intensively developed; however, the selectivity of glycerol conversion to 1,3-PD is still limited.
Selective hydrogenolysis of glycerol into 1,3-PD is much more challenging compared with the
production of 1,2-PD or lower alcohols. The production of 1,2-PD has been studied extensively
since a high yield of 1,2-PD can be obtained under mild reaction conditions [29]. From an
industrial point of view, the production of 1-PO is also very interesting since it finds many
applications as an important industrial intermediate; however, the production of 1-PO from
glycerol has not received much attention. Therefore, the development of a new process for the
efficient conversion of glycerol into propanediols and 1-PO will contribute to new “green”
chemicals which will benefit the environment and make the biodiesel process more profitable.
Until now among these alcohols only the product of 1,2-PD has been commercialized so there is a
huge opportunity for the development of new process for 1-PO.
Figure 1-3 The market value of different value-added products from glycerol in 2016 [28a]
8
1.5 Uses of 1,2-Propanediol, 1,3- Propanediol and 1-Propanol
1.5.1 1,2-Propanediol
1,2-propanediol (1,2-PD) which is a clear colorless viscous liquid is an important medium-value
commodity chemical having a wide range of applications. It is used for making polyester resins,
liquid detergents, pharmaceuticals, cosmetics, tobacco humectants, flavor and fragrance agents,
personal care items, paints, animal feed, antifreeze compounds, etc. There has been a rapid
expansion of the market for 1,2-PD as antifreeze as a de-icing agent due to the growing concern
over the toxicity of ethylene glycol based products to humans and animals. 1,2-PD is
conventionally produced by the hydration of propylene oxide [12]. The process based on a glycerol
feedstock has been recognized as an economically, environmentally and sustainable method
compared with the commercial petroleum-based route.
1.5.2 1,3-Propanediol
1,3-propanediol (1,3-PD) which is a colorless liquid with a freezing point of -24ºC and a boiling
point of 214ºC has many uses. 1,3-PD is generally used as an industrial building block for
producing polymers and composite materials; it is especially used as a monomer in the synthesis
for new types of polyesters such as polytrimethylene and terephthalate. It has also found an
application as a chemical intermediate in the manufacture of cosmetics, medicines and heterocyclic
compounds [30]. Many products that may also contain 1,3-PD include adhesives, sealants,
laminates, coatings, paints, perfumes, fragrances, personal care products and laboratory scale
chemicals [31]. One of the most successful applications of 1,3-PD is the formulation of corterra
polymers [32]. Industrial production of 1,3-PD is currently based on petroleum by
hydroformylation of ethylene oxide or hydration of Acrolein [33]. As petroleum feedstocks
become more limited and costs become higher, glycerol as a bio-feedstock has become a more
attractive feedstock for 1,3-PD production. The production of 1,3-PD from bio-based glycerol has
the potential to become an alternative for current industrial production based on petroleum
feedstocks. Bio-derived 1,3-PD not only offers good market opportunities but also provides a cost
effective method for its production. Many research groups have worked on the selective
hydrogenolysis of glycerol to 1,3-PD; however, selective production of 1,3-PD from biomass-
derived glycerol is still a challenge.
9
1.5.3 1-Propanol
1-Propanol (1-PO) which is a highly flammable, volatile, clear, colorless liquid with an alcohol-
like, sweet and pleasant odor [33] is a major component of resins and is used as a solvent in the
pharmaceutical, paint, cosmetics and cellulose ester industries [34,35]. Production and uses of 1-
PO are associated with its transformation into related compounds such as propionic acid,
propionaldehyde and trihydroxymethyl ethane, all of which are important chemical commodities.
It also finds applications in the manufacture of flexographic printing ink and textiles [36,37], as a
dispersing agent for cleaning preparations and floor wax, metal degreasing fluids, adhesives[38],
a chemical intermediate in the manufacture of other chemicals[39]. More recently, it is being used
as a hand disinfectant by health care workers. Besides its industrial uses, 1-PO is added to foods
and beverages as a flavor (IPCS 1990). 1-PO can be esterified to yield diesel fuels and be
dehydrated to yield propylene, which is currently derived from petroleum as a monomer for
making polypropylene [40]. In addition, like the more familiar aliphatic alcohols of methanol,
ethanol and butanol, 1-PO is considered as a potential high-energy biofuel. The use of 1-propanol
recently has shown potential as the next-generation gasoline to petroleum substitute [35] which
has promoted interest in its production. 1-PO is considered to be a better biofuel than ethanol since
it has advantages over ethanol in terms of higher octane number, tends to have a higher energy
content, lower hygroscopicity, water solubility, energy density, combustion efficiency, storage
convenience. It is compatible with existing transportation infrastructures and pipelines [41] and is
suitable for engine fuel usage [42]. However, the production of propanol is more difficult than that
of other alcohols so up until now it has been too expensive to be a common fuel. In the
petrochemical industry, 1-PO is currently produced via hydroformylation of ethylene to form
propanal followed by hydrogenation to 1-PO [43]. It can also be recovered commercially as a by-
product via the high pressure synthesis of methanol from carbon monoxide and hydrogen or by
the vapor-phase oxidation of propane and from the reduction of propene-derived Acrolein. 1-PO
recently has been obtained from glycerol by conversion of glycerol to 1,2-PD first, with 12-PD
being subsequently converted to 1-PO [44-46]. In comparison with the process based on
petroleum-derived ethylene, propylene, the production of 1-PO based on bio-based glycerol would
be preferential in terms of sustainability and environmental efficiency.
10
1.6 Research objective
Selective conversion of glycerol to green valueable chemicals such as 1,3-PD, 1,2-PD and 1-PO
is promising. In recent years, although significant work has been done towards glycerol
hydrogenolysis to propanediols, the one-pot hydrogenolysis of glycerol to 1-PO has received
limited attention. Therefore, the main focus of the research is to develop a selective catalyst for
the hydrogenolysis of glycerol to green sustainable chemicals, especially the one pot synthesis of
1-PO. The hydrogenolysis of glycerol requires an acidic site for dehydration and a metal site for
hydrogenation. HPAs are well known to be green, active catalysts for many of homogeneous and
heterogeneous acid catalyzed reactions, in particular alcohol dehydration. Hence it is chosen as an
acidic component for this research. The much lower price of Ni compared to noble metals is very
attractive for a hydrogenation. This research work is devoted to the glycerol hydrogenolysis with
the development of catalysts for the one-pot catalytic transformation of glycerol to high value-
added chemicals over a Ni-based HSiW supported catalysts in a water media. Replacement of
homogeneous hazardous catalyst by using as a solid, green catalyst, the use of water as green,
cheap solvent will enable a greener chemical process. To my knowledge, this is the first time a bi-
functional catalyst of Ni and HSiW supported on Al2O3 was successfully prepared and used for
the one-pot production of 1-PO from glycerol in water media using a batch reactor.
Although HPAs have high acidity and high catalytic activity, the high solublility in polar solvents
such as water, the low surface area and the tendency to lose active sites and deactivation under
thermal treatments leads to limitation their application. Therefore the effect of the thermal
treatment on the stability and product selectivity in the glycerol hydrogenolysis is emphasized.
The addition of Cs+ to the catalsyt was also explored since Cs+ is known to modidfy the acidity
of the HPAs. The effect of oxide supports for the HPAs was also explored as the supports could
affect the surface area and the acidity of the catalysts. The catalsyt development work for the
research project are elaborated in the following 3 projects described below.
In the first project, a 10Ni/30HSiW/Al2O3 catalyst (loaded with 10 wt% Ni and 30 wt% on
Al2O3) was prepared and used for the hydrogenolysis of glycerol to lower alcohols such as 1,2-
PD, 1,3-PD and 1-PO using a stainless steel batch reactor. The effect of different metals such as
Pd, Pt and Cu on the catalyst activity was studied. Since a balance of metal and acidity can improve
the performace of catalyst, Cs+ was used to tune the acidity of the catalyst.
11
In the second project, the effect of different process parameters such as catalyst loading, H2
pressure, glycerol and water concentration, temperature on the glycerol conversion and product
selectivity were investigated. Some chemicals, notably acids, can affect the the surface of stainless
steel reactor. Since a supported strong acid, HPA, was part of the catalyst used for the research, a
Hastelloy reactor was used for the investigation of the effect of process parameters on the catalytic
performance of the 10Ni/30HSiW/Al2O3 catalyst.
In the third project, the affect of different factors on the properties of the heteropolyacids itself
such as different Keggin type heteropolyaicds, the thermal treatment and the support were
investigated.
Various characterization techniques such as BET, XRD, TPR, TPD, TGA and FTIR were used to
characterize the catalysts. The properties of the catalysts were used to explain the reactivity of the
catalysts for the conversion and selectivities between the catalyst structure and the catalytic
performance. A reaction pathway for the hydrogenolysis of glycerol to various products was
proposed.
Finally, conclusions are drawn and recommendations are given for future work based on the results
of these studies.
12
Chapter Two
Literature Review
2.1 Introduction
The excess of waste glycerol produced in the biodiesel industry may be used for the production of
value-added chemicals to avoid waste disposal and increase process economy. Various reactions
are available to derive value added chemicals of commercial interest from glycerol. Because of the
high functionality of glycerol (two primary and one secondary hydroxyl groups), reactions can
proceed along multiple reaction pathways to give mixtures of products. Therefore, careful
development of catalysts and reaction conditions is of great importance to selectively obtain the
desired products. The biodiesel industry currently regards glycerol as a waste by-product;
however, with novel methods glycerol has the potential to be converted into other valuable
products. Some of these value-added products are 1,2-PD, 1,3-PD and 1-PO. A literature review
on reaction mechanism, hydrogenolysis of glycerol into these value-added chemicals using
different catalysts is discussed in this section.
2.2 Reaction mechanism for the heterogeneous hydrogenolysis of glycerol to
lower alcohols
It is proposed that the hydrogenolysis of glycerol occurs via several parallel and consecutive
reaction pathways, leading to a range of products such as 1,2-PD, 1,3-PD, 1-PO, 2-propanol, EG,
lactic acid, ethanol, methanol. Therefore, it is a great challenge to design catalysts that can give a
high yield of the desired products, especially 1,3-PD. In order to develop efficient catalysts, it is
of great importance to understand the reaction mechanism since it can help to design further new
catalysts and provide information for process optimization.
According to previous studies, there are some possible mechanisms for the production of lower
alcohols such as 1,2-PD, 1,3-PD and 1-PO. The production of 1,2-PD or 1,3-PD was intensively
studied and some possible pathways were proposed: the dehydration – hydrogenation mechanism
and the dehydrogenation – dehydration – hydrogenation mechanism. In addition, the direct
hydrogenolysis mechanism, the chelation – hydrogenolysis mechanism and the etherification –
13
hydrogenation mechanism have also been proposed. The dehydration – hydrogenation mechanism
involves the dehydration of glycerol to acetol or 3-hydroxypropionaldehyde (3-HPA) and
subsequent hydrogenation of these aldehydes to 1,2-PD or 1,3-PD (Scheme 2-1). The dehydration
– hydrogenation pathway is usually feasible under acidic conditions where acid sites exist in the
catalytic system [47-51]. The dehydration step occurs at the acid sites, and the hydrogenation step
is catalyzed by the metal. According to this mechanism, most previous studies show that the
reaction favors the formation of 1,2-PD. It was shown that generally the tungsten component is
necessary to promote the selectivity to 1,3-PD since it is probably beneficial to induce BrØnsted
acid sites that can cleave the secondary – OH group in glycerol.
Scheme 2-1 Dehydration – hydrogenation mechanism for the hydrogenolysis of glycerol [48]
While the dehydration – hydrogenation mechanism is usually feasible in the presence of acid sites,
the dehydrogenation – dehydration – hydrogenation mechanism (Scheme 2-2) is more dominant
when the glycerol hydrogenolysis reaction is performed under basic conditions. The metal catalyst
serves both dehydrogenating and hydrogenating functions in the total reaction process. It has been
pointed out by Feng et. al. [52] that the production of 1,3-PD seems to be very difficult under basic
conditions.
Scheme 2-2 Dehydrogenation – dehydration – hydrogenation mechanism for the hydrogenolysis
of glycerol to 1,2-PD [52]
Tomishige et al. developed a metal – acid bifunctional catalyst system, which exhibited good
performance for the hydrogenolysis of glycerol [47, 50]. He proposed that the mechanism of
14
glycerol hydrogenolysis using Rh–MOx/SiO2 and Ir–MOx/SiO2 (M = Re, Mo or W) catalysts [49,
51, 53]. A model of the transition state in the glycerol hydrogenolysis to 1,3-PD using Ir –
ReOx/SiO2 is shown in Scheme 2-3. First, glycerol is adsorbed on the surface of a ReOx cluster at
the CH2OH group to form a terminal alkoxide. Meanwhile, hydrogen is activated on the Ir surface
to form a hydride species. Next, the alkoxide located at the interface between ReOx and the Ir
surface is attacked by the hydride species, and the OH– groups in the alkoxide are eliminated by
releasing a water molecule. Finally, the hydrolysis of the reduced alkoxide gives the diol products.
Scheme 2-3 Direct hydrogenolysis mechanism for the hydrogenolysis of glycerol to 1,3-PD over
Ir-ReOx/SiO2 catalyst [51]
Besides the direct reaction mechanism, Qin et al. [54] and Liu et al. [55] proposed a different direct
hydrogenolysis mechanism using WOx-supported Pt catalysts. This direct hydrogenolysis
mechanism is distinguished by the heterolytic cleavage of hydrogen molecules to protons (H+) and
hydrides (H–) at the interface of WOx and Pt. The strong interaction between Pt and WOx
facilitates the heterolytic dissociation of hydrogen molecules. The proton formed will attack the
primary or the secondary OH– group in the glycerol molecule by a protonation – dehydration, and
form an intermediate oxocarbenium ion(I) or oxocarbenium ion(II), which is subsequently
attacked by a proton (H+) to form 1,2-PD or 1,3-PD, respectively (Scheme 2-4).
Scheme 2-4 Direct hydrogenolysis mechanism for the hydrogenolysis of glycerol to Propanediols
over Pt/WOx catalyst [54,55]
15
Chaminand et al. in 2004 [56] proposed a chelation – hydrogenolysis mechanism. It is suggested
that the active metals (M) can be chelated by two hydroxyl groups from the glycerol molecule and
thus modify the selectivity of the hydrogenolysis reaction. While 1,2-PD can be obtained via a 5-
membered-ring chelation transition state, 1,3-PD can be obtained via a 6-membered-ring chelation
transition state (Scheme 2-5).
Scheme 2-5 Chelation – hydrogenolysis mechanism [56]
Wang et al. has proposed glycidol as an intermediate from the glycerol dehydration on acid sites.
Using Cu-based catalysts Wang et al. [57] and Huang et al. [58] discovered evidence for the
formation of glycidol (3-hydroxy-1,2-epoxypropane). Therefore, Feng et al. [52] proposed an
etherification – hydrogenation mechanism for the hydrogenolysis of glycerol to propanediols. As
shown in Scheme 2-6, glycidol is formed by the intramolecular etherification of two adjacent OH–
groups in the glycerol molecule. Hydrogenation of glycidol via a ring-opening reaction can
produce propanediols.
Scheme 2-6 Etherification – hydrogenation mechanism [52]
1-Propanol (1-PO) is another valuable chemical produced from the hydrogenolysis of glycerol;
however, the direct conversion of glycerol to 1-PO remains essentially unexplored. Some possible
ways for the conversion of glycerol to 1-PO have been proposed through either propanediols or
acrolein as an intermediate: further hydrogenolysis of propanediols or hydrogenation of acrolein.
16
Miyazawa et al., [59] studied the reaction scheme of glycerol hydrogenolysis and degradation over
Ru/C + Amberlyst and Ru/C catalyst in the aqueous solution. It is assmued that 1-PO is formed
via 1,3-PD (Scheme 2-7).
Scheme 2-7 Reaction scheme of glycerol hydrogenolysis and degradation reactions [59]*
*Reprinted from Miyazawa T. et al., J. Catal., 2006, 240, 213–221 with permission from Elsevier
Gandarias et. al., [50] proposed the hydrogenolysis of glycerol over Pt supported on an amorphous
silica-alumina (Pt/ASA) (Scheme 2-8): glycerol is first dehydrated to either acetol or 3-HPA which
is hydrogenated to 1,2-PD or 1,3-PD respectively with further hydrogenolysis of 1,2-PD or 1,3-
PO to form 1-PO.
Scheme 2-8 The hydrogenolysis of glycerol over Pt supported on an amorphous silica–alumina
(Pt/ASA) [50]
Lin et. al. [60] used a sequential zeolitic packing and a Ni based catalysts as two-layer catalysts in
a fixed-bed reactor to study the hydrogenolysis of glycerol and indicated most of 1-the PO in the
products was generated from glycerol via a “sequential two-time dehydration-hydrogenation”
17
mechanism, with most of 1-PO coming from the hydrogenation of acrolein that was produced from
the two-time dehydration of glycerol. Using sequential two-layer catalysts (zirconium phosphate
layer was packed in the upper layer, the supported Ru catalysts were in the second layer) in a
continuous-flow fixed-bed reactor for the conversion of glycerol to 1-PO, Wang et. al. [61]
proposed the possible reaction route involved in glycerol hydrogenolysis. It was found that the two
sequential-layers catalyst system can convert glycerol to 1-PO at complete glycerol conversion by
a dehydration– hydrogenation route, where ZrP converted glycerol into acrolein while Ru/SiO2
catalyst transformed acrolein into 1-PO.
Yu et al., investigated the hydrogenolysis of glycerol to 1-PO in aqueous solutions using the
catalyst of Ir/ZrO2 [62] and confirmed in two separate experiments that the formation of 1-PO
directly from 1,2-PD occurred at a considerably higher rate than that from 1,3-PD, and verified
that 1-PO was mainly produced by the formation of 1,2-PD as an intermediate during the reaction.
This pathway was also proposed by Sun et al. [81b] when they studied vapor-phase catalytic
conversion of glycerol into propylene over WO3/Cu/Al2O3 catalyst (Scheme 2-9).
Scheme 2-9 Proposed reaction routes involved in glycerol hydrogenolysis over Ir/ZrO2 catalyst
[63]
Nakagawa Y. et al., [64] explained the formation of 1-PO using the metal–acid bifunctional
catalyst system where the acid function plays a role in the dehydration reaction and the metal
catalyzes the hydrogenation reaction (Scheme 2-10). It is assumed that the protonation of the
secondary OH in glycerol and subsequent dehydration produces a more stable cationic
intermediate than the protonation of terminal OH produces. The deprotonation of the cationic
intermediates produces more 3-hydroxypropanal than acetol, although thermodynamically 3-
18
hydroxypropanal is less stable than acetol. The subsequent dehydration of 3-hydroxypropanal
produces acrolein and finally 1-PO.
Scheme 2-10 Elementary reactions in the dehydration of glycerol [64]*
*Reprinted from Nakagawa Y. et al., Catal. Sci. Technol., 2011, 1, 179–190 with permission from the Royal Society
of Chemistry
An enormous number of catalysts have been reported for the conversion of glycerol to lower
alcohols. In this section, the literature reporting different types of catalyst are reviewed. The
reported experimental results are listed in Table A in Appendix A.
2.3 Heteropolyacids
Heteropolyacids (HPAs) present several advantages as catalysts that make them economically and
environmentally attractive [65, 66]. HPAs are very strong BrØnsted acids, stronger than common
inorganic acids (HCl, H2SO4…) and are even sometimes classified as super acids [50]. Morever
their acid‒base and redox properties can be tuned by modifying their compositions. With a strong
Brønsted character, approaching the superacidic region, HPAs represent a potential alternative to
other acid systems and become the most interesting ones from a catalysis and industrial point of
view.
Among the HPAs, the best known of these structures is the Keggin‒type heteropolyacids. The
Keggin‒type heteropolyacids typically represented by the formula XM12O40n- where X is the
central atom or heteroatom, M (with M=W, Mo, V..) is the addenda atom and X (with X=P, Si, Ge
or As) is the charge of the heteropoly anion itself (Fig. 1-4). The acidity of the HPAs strongly
depends on the nature of the addenda atoms. The BrØnsted acidity strongly decreases with the loss
of constitutional water because all the residual protons are then localized (Fig. 1-5). The exchange
19
of the protons of the heteropoly acid by cations results in a decreased number of BrØnsted acid
sites. One important drawback of Keggin-type HPAs is their low specific surface area, a
disadvantage which can be overcome by dispersing the HPAs on high surface area supports. The
thermal stability is also influenced by the interaction between the heteropolyacids and the carrier
substrate [67-69]. When using supported heteropoly acids, the acidity also depends on the support
due to electro-static interactions.
Figure 2-1 Crystal structure of a typical Keggin-type heteropolyanion. (left) Ball-and-stick
model; (right) polyhedral model [70] *
*Reprinted from Zhou Y. et al, Catal. Sci. Technol., 2015, 5, 4324-4335 with permission from the Royal Society of
Chemistry
Figure 2-2 Models proposed for the states of acidic protons and water in solid H3PW12O40 [71]*
*Reprinted from Misono M., Chem. Commun., 2001, 1141–1152 with permission from the Royal Society of
Chemistry
20
Although HPAs have good thermal stability in the solid state, better than other strong acids like
ion exchange resins [65], the tendency to decompose the Keggin structure under thermal
treatments always leads to the loss of active sites and deactivation [72-75]. Several ways of
enhancement of the stability of the HPAs have been investigated. One way consists in the
aforementioned exchange of addenda metal atoms. The second way consists of the preparation of
HPA salts, which are known to be more stable than their parent acid due to the reduced number of
protons needed in the final decomposition step of the HPA. Some studies were focused on the
influence of the support on the thermal stability of the HPA. Apparently, Lewis acid supports (e.g.
alumina, zirconia) increase the thermal stability of the HPA by electrostatic interactions [76].
Therefore, the properties of HPAs can be tuned via the proper selection of the central atom, the
addenda atom, the counter-cations and the support to make the catalysts feasible.
2.4 Catalyst for production of 1,3-Propanediol from glycerol
Several patents and papers have disclosed 1,3-PD production by the catalytic hydrogenolysis of
glycerol in the presence of homogeneous or heterogeneous catalysts. In this section the available
literature on the heterogeneous catalysts used for production of 1,3-PD from glycerol is presented.
2.4.1 Promoting effect of Tungsten-added catalysts in the generation of BrØnsted acid
Several research groups have pointed out the importance of BrØnsted acid sites in 1,3-PD
formation and it has been found that the 1,3-PD yield is approximately proportional to the
concentration of the BrØnsted acid sites since the BrØnsted acid sites favor the removal of the
secondary hydroxyl group of glycerol to 3-hydroxypropionaldehyde, which subsequently is
hydrogenated by mainly Platinum to form 1,3-PD [77-87].
It is reported that Tungsten (W) compounds are widely used in various industrial processes such
as oxidations, acid–base reactions, and photocatalytic reactions. The acidity of W oxide species
has been proposed as playing a key role in the selective production of 1,3-PD [77,54,56,82,88]. It
was found that H atom spillover onto the WOx species forming W6-nOx–(nH+) as BrØnsted acid
centers under the reaction conditions. H2 can restore the BrØnsted acid sites by reduction of WOx
species or by formation of acidic HxWO3 species. H atoms formed by H2 dissociation become
involved not only in desorption of adsorbed intermediates, but also in the generation and
maintenance of the BrØnsted acid sites [83, 89, 90, 91]. In 2010 Gong et al. [82] prepared SiO2-
21
supported Pt/WO3/TiO2 catalysts. It was found that the main role of WO3 is to regulate acidity of
the catalyst by introducing BrØnsted acid sites, which were shown to be essential for 1,3-PD
formation. The optimal loadings of Ti and W as oxides were 10% and 5%, respectively, and the
glycerol conversion and 1,3-PD selectivity reached 15.3% and 50.5%, respectively.
Heteropolyacids (HPAs) that possess unique properties such as BrØnsted acidity, uniform acid
sites and easily tunable acidity [92-94] compared to conventional solid acid catalysts such as
oxides or zeolites make them economically, environmentally attractive [65,66]. Morever their
acid‒base and redox properties can be tuned by modifying their compositions. HPAs have found
many applications in the field of catalysis and the best known of these structures is the Keggin‒
type heteropolyacids. Among the HPAs, silicotungstic acid (HSiW) has been intensively
investigated for the conversion of glycerol to propanediols since in the presence of water, HSiW
having a lower oxidation potential and higher hydrolytic stability, is superior to other HPAs as a
catalyst in a water medium [95]. HSiW is reported to be responsible for inducing the presence of
BrØnsted acid sites [77,96,97]. In 2012 Zhu et. al. [77] reported that supporting HSiW on Pt/SiO2
has increased the acid sites, especially BrØnsted acid sites and it is obvious that BrØnsted acid sites
are indispensable in order to produce 1,3-PD selectively. With the optimized catalyst of Pt-
HSiW/SiO2 and optimized conditions, glycerol conversion and 1,3-PD selectivity reached 81.2%
and 38.7%, respectively for reactions carried out in a aqueous phase. In 2013, Zhang et. al. [83]
developed a new method to synthesize mesoporous Ti–W oxides and investigated how tungsten
oxide species affect catalyst texture. It was reported that the presence of strong BrØnsted acid sites
was suggested to be responsible for the superior performance for selective hydrogenolysis of
glycerol to 1,3-PD. The excellent performance was attributed to the presence of a large amount of
acid sites; in particular the BrØnsted acid site. The catalyst 2Pt/Ti90W10 exhibited high selectivity
to 1,3-PD of 40.3% and promising catalytic activities (18.4% glycerol conversion) at 180oC, 5.5
MPA of hydrogen. In 2013 Zhu. Et. al. [79] carried out the hydrogenolysis of glycerol over zirconia
supported bifunctional catalysts containing Pt and HPAs. Among the tested supported HPAs
catalysts, HSiW exhibited superior performance. Addition of HSiW to Pt/ZrO2 catalysts improved
the catalytic activity (24.1% conversion) and 1,3-PD selectivity (48.1%) remarkably because of
the enhanced BrØnsted acid. In the same year Zhu et. al. [86] reported that addition of alkaline
metals Li, K, Rb and Cs was a powerful approach to tune the acidic property of HSiW in terms of
22
BrØnsted acid sites and Lewis acid sites and to control the catalytic performance in glycerol
hydrogenolysis.
2.4.2 Noble metal based catalysts
Since hydrogenolysis uses hydrogen as a reactant for the hydrogenation, the hydrogenolysis
catalyst must have an ability to activate hydrogen molecules. Noble metals are well known to be
able to activate hydrogen molecules and are widely used in hydrogenation catalysts.
2.4.2.1 Rh based catalyst
Supported Rh catalysts show some activity in the reforming of aqueous glycerol to 1,3-PD. In
2004, Chaminad et al. [56] showed that when using a catalyst of Rh/C with a H2WO4 additive the
selectivity to 1,3-PD was 12% at 32% conversion after 168h and 1,3-PD/1,2-PD molar ratio of 2
from a sulfolane solution of glycerol at a temperature of 453K and pressure of 8 MPa hydrogen.
In 2005, Kusunoki et al. [47] also reported that the addition of H2WO4 to Rh/C enhanced the
glycerol conversion and the selectivity to 1,3-PD, however, the activity was not so high. The
selectivity to 1,3-PD was 20.9% at a conversion of 1.3% using 20w% glycerol aqueous, and initial
H2 pressure 8.0 MPa at 453K. In 2006, Miyazawa et. al. [59] tested the activity over M/C and M/C
+ Amberlyst catalysts (M = Pt, Rh, Pd, and Ru) for the reaction of glycerol. Among these catalyst,
Rh-based + Amberlyst catalyst gave the highest selectivity to 1,3-PD of 9% at a conversion of 3%
under the condition of 393K and 8MPa hydrogen. In 2007, Furikado et al. [48] compared the
activity of various supported noble-metal catalysts (Rh, Ru, Pt and Pd over C, SiO2 and Al2O3) for
the hydrogenolysis of aqueous glycerol at a much lower temperature of 393K. Among the catalysts
tested, Rh/SiO2 gave the highest glycerol conversion and selectivity to 1,3-PD (7.2% and 7.9%
respectively).
2.4.2.2 Pt based catalyst
Supported Pt catalysts are some of the most active supported catalyst for the hydrogenolysis of
glycerol to 1,3-PD and have been intensively studied by many researchers for the reforming of
glycerol to 1,3-PD. In 2010 Gandarias et al. [50] reported the hydrogenolysis of aqueous glycerol
over a platinum catalyst supported on acidic amorphous silica-alumina. At 493K and 4,5 MPa H2
pressure, the selectivity to 1,3-PD was 4.5% at a conversion of 19.8%. In 2010, Qin et al. [54]
23
applied Pt/WO3/ZrO2 catalysts for the hydrogenolysis of aqueous glycerol. Both the amounts of
W and Pt greatly affected the performance. The highest activity was 46% for 1,3-PD selectivity
and 72% of the glycerol conversion was obtained with the catalyst of 3w%Pt and 10w%W. In
2011, Oh et. al. [84] reported very selective 1,3-PD formation using a Pt sulfated zirconia. Using
this catalyst under the condition of 443K for 24h with an initial H2 pressure of 7.3 MPa, an 84%
1,3-PD selectivity was observed at 66.5% glycerol conversion in 1,3-dimethyl-2-imidazolidinone
(DMI) solvent. In 2012, Mizugaki et. al. [98] investigated the addition effect of a secondary metal
on a Pt/WO3 catalyst. Among the additive metals tested (Al, V, Cr, Mn, Fe, Zn, Ga, Zr, Mo and
Re), Al showed the best effect in performance for glycerol hydrogenolysis to 1,3-PD (44%
selectivity at 90% conversion after 10h at 453K and 3MPa hydrogen in water without any
additives). It was suggested that the positive effect of Al was related to the high performance of
Pt–W catalysts on the Al-based supports. In 2013, Dam et al. [99] tested the effect of various
tungsten-based additives for glycerol hydrogenolysis over commercial catalysts (Pd/SiO2,
Pd/Al2O3, Pt/SiO2 and Pt/Al2O3) in water at 473K. The highest conversion and selectivity (49%
conversion, 28% selectivity) to 1,3-PD was achieved by using a Pt/Al2O3 + HSiW catalyst at 473K
and 4MPA hydrogen after 18 hours. In 2013, Arundhathi et. al. [100] reported a very good result
using Pt/WOx on a boehmite (AlOOH) support. The 1,3-PD yield reached 66–69% after 12h at
453K and 5MPa hydrogen from aqueous glycerol and these values are the highest reported up until
now. In 2013, Delgado [101] studied the influence of the nature of the support on the catalytic
properties of Pt-based catalysts for the hydrogenolysis of glycerol. It was found that 1,3-PD is
formed only under H2 and should be produced from 3-HPA hydrogenation; the aldehyde being
easily hydrogenated and never observed under their experimental conditions. It is important to
mention that a noticeable formation of H2 occurred under a N2 atmosphere, providing aqueous
phase reforming of glycerol on the Pt sites. Although titania is the best catalyst for the production
of 1,2-PD under the reaction conditions studied, alumina is the most active catalyst for the
production of 1,3-PD under a hydrogen atmosphere. It has been reported that under N2, the alumina
supported catalyst yielded the highest amount of H2, and this catalyst can also give the most 1,3-
PD under H2 (at a conversion of 10%, the selectivity was 12.1%). Longjie et. al. [55] prepared a
Pt catalyst supported on mesoporous WO3 which gave 39.3% of 1,3-PD selectivity at 18%
conversion. The activity and selectivity were much higher than those of Pt/commercial WO3
catalysts (29.9% selectivity and 4.5% conversion). In 2013 Zhu et. al. [78] reported that catalysis
24
of 2Pt–15HSiW/ZrO2 for glycerol hydrogenolysis. Although this study focused on the production
of propanols, good 1,3-PD selectivity was obtained (~40% selectivity at ~60% conversion at 433K,
5MPa, 10wt% of aqueous glycerol). In 2014 the same group [102] prepared a series of SiO2
modified Pt/WOx/ZrO2 catalysts with various SiO2 content for glycerol hydrogenolysis to improve
1,3-PD selectivity. Among them, the 5PtW/ZrSi catalyst showed superior activity and provided
maximum 1,3-PD selectivity,of up to 52.0% at a conversion of 54.3% at 180oC, 5.0 MPa. Pt–
HSiW/ZrO2 was further improved by modification with alkali metals (Li, K, Rb and Cs) [79].
Among them, Pt–LiHSiW/ZrO2 showed a higher activity and 1,3-PD selectivity than the
unmodified catalyst, attaining 43.5% conversion and 53.6% 1,3-PD selectivity at 453K. In 2014,
Deng et al. [103] investigated the particle size effect of a series of carbon nanotubes (CNTs)
supported Pt-Re bimetallic catalysts for glycerol hydrogenolysis. It was found that the scission of
the secondary C–O bond of glycerol was favored over larger sized Pt-Re/CNTs catalysts, leading
to the formation of 1,3-PD. Under a temperature of 170oC and 4 MPA hydrogen, after 8 hours, the
conversion was 20% and the selectivity to 1,3-PD was 13%.
2.4.2.3 Ru based catalyst
In comparison to Pt and Rh, Ru added catalysts are less active for the conversion of glycerol to
1,3-PD. In 2014, Vanama P.K., et al. [104] reported on the catalytic behavior of Ru/MCM-41
catalysts for the hydrogenolysis of glycerol in the vapor phase at 230oC. It was found that the
conversion of glycerol was 62% and the selectivity to 1,3-PD was 20% with a ruthenium loading
of 3 wt%.
2.4.2.4 Non-noble metal based catalysts
For the hydrogenolysis of glycerol to 1,3-PD; since 3-HPA is an unstable intermediate that easily
further dehydrates to acrolein it is often preferred to use noble metals for the hydrogenation of 3-
HPA to 1,3-PD. Non-noble metals are rarely used for the hydrogenolysis of glycerol to 1,3-PD
and there are only a few papers that have been published on this topic. In 2009 Huang L. et al.
[105] prepared a Cu–HSiW/SiO2 catalyst and applied it for the vapor-phase hydrogenolysis of
glycerol. At optimum conditions (483K, 0.54 MPa H2, without water), conversion and 1,3-PD
selectivity reached 83.4% and 32.1%, respectively. It was found that the presence of water
decreased both the activity and 1,3-PD selectivity of the Cu–HSiW/SiO2 catalyst. In 2011, Feng
25
et. al. [106] studied the gas phase hydrogenolysis of glycerol using a series of Cu/ZnO/MOx
catalysts (MOx=Al2O3, TiO2, and ZrO2) at 240–300◦C under 0.1MPa of H2. The Cu/ZnO/TiO2
catalyst favored the formation of 1,3-PD with a maximum selectivity of 10% at a high reaction
temperature of 280oC. The results showed that the selectivity to 1,3-PD increased with increasing
reaction temperature. It was suggested that the weak acid sites favor the dehydration of glycerol
to 3-hydroxypropanal (3-HPA), resulting in the formation of 1,3-PD and the strong acid sites favor
the dehydration of glycerol to hydroxyacetone, which can be hydrogenated to 1,2-PD. More
reported numerical results regarding this process are listed in Table A-2 in Appendix A.
2.5 Catalysts for production of 1-Propanol from glycerol
The initial goal of the present work was the investigation and development of heterogeneous
catalysts for the hydrogenolysis reaction of glycerol to 1,3-PD. During the development, a catalyst
was discovered surprisingly to catalyze the reaction with high yield of 1-PO from glycerol. 1-PO
was identified as a side product during the overhydrogenolysis reaction of glycerol to diols and so
far not much work has been carried out on this topic. In 2007 Furikado et al. [48] achieved high
selectivity of 41.3% to 1-PO over Rh/SiO2 at 120°C and 8.0 MPa in the presence of Amberlyst
during glycerol hydrogenolysis. In 2008 Kurosaka et al. [88] reported a significant amount of 1-
PO (28% yield) was formed using Pt/WO3/ZrO2 in 1,3-dimethyl-2-imidazolidinone at 130°C and
4.0 MPa hydrogen; probably because of the severe reaction conditions employed. In 2010 Quin
L.Z. et al. [54] reported that a 56.2% yield of 1-PO was obtained in a fixed bed reactor using the
catalyst 4.0Pt/WZ10 (containing 10 wt% tungsten and calcined at 700◦C) at 130oC and 4 MPa H2.
It was assumed that the production of 1-PO could increase if the reaction pressure and calcination
temperature were increased. The deoxygenation of glycerol is proposed to occur by an ionic
mechanism, involving proton transfer and hydride transfer steps. The excess amount of protons
and hydride ions may enhance the consecutive deoxygenation of propanediols to propanols. In
2010, 2011 Tomishige et al. [53, 107] reported that 1-PO can be obtained with a yield of 20.72%
and 23.9% respectively by using Ir/SiO2 modified with a Re species and sulfuric acid additive at
120C and 8MPa hydrogen. In 2011 Thibault et al. [108] obtained a 18% yield to 1-PO from
glycerol hydrogenolysis at 200°C and 3.45 MPa hydrogen using a homogenous Ru complex and
methane sulfonic acid in a water–sulfolane mixed solvent. In 2011, Ryneveld et. al. [75] reported
that a 42.8% yield of 1-PO could be obtained for the conversion of glycerol using commercial
26
Ni/SiO2 catalysts at 320oC and 6MPa hydrogen. In 2012, Zhu et. al. [77] obtained a 32.7% yield
of 1-PO in the hydrogenolysis of glycerol to 1,3-PD over Pt-HSiW/SiO2 at 200oC and 5MPa
hydrogen. It was found that the selectivity of 1-PO increased linearly with increasing temperature
as the higher temperature facilitated the overhydrogenolysis of propanediols. Following this paper,
in the same year Zhu S. published a paper on the one-step hydrogenolysis of glycerol to
biopropanols using Pt–HSiW/ZrO2 catalysts providing a high yield of 1-PO and 2-PO at 200oC
and 5MPa (80% yield). It was found that with respect to the selectivity, the increase of hydrogen
pressure favored the sequential hydrogenolysis of propanediols to produce propanols. Using Ni
instead of Pt, Zhu et. al. reported that the yield of 1-PO was rather low, only 4% [78]. Generally,
the catalysts that are effective for the selective hydrogenolysis of glycerol to 1,3-PD have a
potential for the production of 1-PO from glycerol. However, these systems need a high pressure
of hydrogen and Rh-based or Pt based catalysts are expensive. Although Ni, a nonprecious metal
can also be used for hydrogenation reactions [75, 109-112], the use of supported Ni catalysts for
the chemical transformation of glycerol to 1,3-PD and 1-PO has appeared less frequently in the
literature and the yield of 1-PO is still low even under severe reaction conditions.
The 1-PO is usually a by-product of glycerol hydrogenolysis to 1,2-PD and 1,3-PD and the yield
of 1-PO is rather low. Recently there are a few reports on the conversion of glycerol-derived
propanediols to 1-PO; however; not much research has been done on the conversion of glycerol to
1-PO directly. In 2010 Amada Y et al reported that using RhReOx/SiO2 (Re/Rh ¼ 0.5) catalyst
can obtain high yields of 1-PO (66%) by the hydrogenolysis of 1,2-PD at 393 K and 8.0 MPa initial
H2 pressure [45]. In 2014 Peng et. al reported a process for the conversion of 1,2-PD to 1-PO over
a ZrNbO catalyst with the selectivity to propanol reaching approximately 39% at 85.0% 1,2-PD
conversion at 290°C under 1 atm N2 ; the weak Brønsted acid sites may play a crucial role in the
conversion of 1,2-PD to 1-PO [113]. In an attempt to elucidate the role of propenediols as the
intermediates to 1-PO in the hydrogenolysis of glycerol Ryneveld et. al. found that using Ni/Al2O3
and Ni/SiO2 catalysts in the hydrogenolysis of 1,3-PD, 1-PO was produced as the main product
[30]. Recently, the sequential two-layer catalysts for the hydrogenolysis of glycerol in continuous-
flow fixed-bed reactor was studied for the production of 1-PO but the selectivity to 1-PO is still
low with maximum selectivity at 69% [60, 61, 63]. More reported numerical results regarding this
process are listed in Table A-3 in Appendix A.
27
Chapter Three
Experimental Apparatus and Methods
In this chapter, the procedure of catalyst preparation and loading of different composition are
introduced. The analytical methods employed in this work are outlined including the quantitative
analysis of liquid products by gas chromatography. The specifications of the batch autoclave
reaction for glycerol hydrogenolysis to produce lower alcohol and the procedures of liquid
sampling are explained. The detailed catalyst characterization techniques are described including
temperature programmed desorption (TPD), X-Ray diffraction (XRD), Thermogravimetric
analysis (TGA), BET surface area and Fourier Transform InfraRed spectroscopy (FTIR).
3.1 Materials
Glycerol (≥99.5%), 1,2-Propanediol (≥98%), 1,3-Propanediol (99%), and 1-Propanol (anhydrous
99.7%) were obtained from Sigma-Aldrich. Ni(II) nitrate hexahydrate (Ni(NO3)2.6H2O,
crystalline, ≥99.0%), Copper(II) nitrate hemi (pentahydrate) (Cu(NO3)2.2.5H2O, ≥98.0%),
Platinum chloride (H2PtCl6.6H2O), Palladium acetate (Pd(OAc)2, ≥98%), aluminum oxide
(corundum, α-Al2O3, 99%, 100 mesh) and Tungstosilicic acid hydrate (H4SiW12O40.nH2O,
anhydrous basis) were purchased from Sigma-Aldrich, Canada. High purity grade hydrogen and
nitrogen were purchased from Praxair Canada and were used directly from the cylinders.
3.2 Catalyst Preparation Methods
In this section, the procedures of preparing catalysts via different preparation methods including
the methods of loading different promoters are introduced.
3.2.1 The preparation of metal heteropolyacids supported catalyst by impregnation
Different metals and supports of the HPAs catalysts were prepared by the incipient wetness
impregnation method similar to that previously described [104].The catalyst support was
impregnated with a desired amount of HPAs aqueous solution by slowly adding small quantities
of the HPAs solution to a well stirred weighed amount of support at room temperature. The mixture
was blended well to ensure the support remained dry throughout the solution addition process
28
(until all the desired amount of HPAs is impregnated). Then the powder was dried at 393 K
overnight and calcined at 623K for 5 h in air. The HPAs/support samples obtained were further
impregnated with an aqueous solution of the metal precusor following: the same procedure as the
previous step to obtain an appropriate amount of metal loading. After drying at 393 K, the samples
were calcined in air at 623K for 5 h. The catalysts are labelled as xM/yHPAs /support, where x, y
represents the nominal weight loading of metal and HPAs respectively. Before carrying out an
experiment the catalyst was reduced in hydrogen for 5 hours.
3.2.2 Loading Cs on 10Ni/30HSiW/Al2O3 catalysts by ion-exchanged method
The 10Ni/30CsxH4-xSiW/Al2O3 catalysts were prepared via ion exchange. A set of cesium-
exchanged HSiWs were prepared by an ion-exchange method with a variation of cesium content.
A known amount of cesium chloride (CsCl, Sigma-Aldrich) was dissolved in distilled water then
the desired amount of 10Ni/30HSiW/Al2O3 was added to this solution and aged for 4 hours without
mixing. After that, the round bottle with the aged solution was evaporated on an oil bath at 70oC
until the solvent evaporated completely. Then the catalyst was dried in an oven at 110oC overnight.
Finally, it was calcined at 350oC for 5 h to yield the 10Ni/30CsxH4-xSiW/Al2O3.
3.3 Autoclave Experimental Apparatus
In this section, the experimental apparatus for the experiments carried out in an autoclave are
introduced including the catalyst reduction and reaction systems.
3.3.1 Catalyst reduction apparatus
Before each experiment was carried out, the catalyst was reduced in a quartz tubular reactor. The
reactor is enclosed by a furnace controlled by a temperature controller as shown in Fig. 3-1. The
pre-weighed catalyst particles were placed on a catalyst bed made from quartz in the tubular reactor
and the reactor was placed into the furnace; a thermocouple was placed into the tube below the
catalyst bed. The reactor was heated to the designated temperature under a continuous high purity
helium flow. After the temperature was reached, the three-way valve was adjusted to let a
continuous high purity hydrogen gas flow upward through the catalyst bed for 5 hours. Then the
furnace was turn off and the catalyst particles were cooled to room temperature under a helium
flow.
29
Figure 3-1 Diagram of the catalyst reduction apparatus
3.3.2 Autoclave apparatus
Two mini bench top reactors made of two different materials which as illustrated in Fig. 3-2 were
used for the catalyst activity tests in this thesis. One is a 300ml Parr Instrument 4182 Series
constructed of Stainless Steel T316 and another is a 300mL Parr Instrument 4560 Series
constructed of hastelloy. The reactors are sealed with a PTFE O-ring seal. The maximum operating
conditions were rated to be 360ºC and 3000PSI. An impeller was connected to a magnetic drive
for mixing. The reactor temperature was monitored with a thermocouple and the temperature was
controlled by a Parr Instrument 4848 Series (for hastelloy reactor) and Parr Instrument 4842 Series
(for Stainless Steel T316) reactor controller. Over-pressure protection was provided by a rupture
disk made from Au and rated to fail at 2500 psi purchased from Fike Corp. A sampler was equipped
for taking liquid samples at different time intervals during the reaction.
Figure 3-2 An autoclave reactor system
H2 in
H2 out
30
3.4 Products Analytical Apparatus and Method
In this section, the apparatus for products analysis and the mathematic analytical method are
introduced.
3.4.1 Gas Chromatography (GC)
Reaction product samples were taken at different time intervals during the reaction, cooled to room
temperature, and were firstly centrifuged using an IEC CL31 multispeed centrifuge purchased
from Thermo Electron Corp. at 8000RPM for 10 minutes to separate the large catalyst particles
from the liquid product samples. Then the centrifuged liquid samples were filtered through a
polyethersulfone syringe membrane with 0.2μm pore size to further separate the fine particles
remaining in the liquid samples. These samples were analyzed by an Agilent Technoloies 6890N
Gas Chromatograph equipped with a flame ionization detector (FID). All the samples were
injected automatically by an Agilent Technologies 7863 Series auto-injector with a 5μL syringe.
A J&W Scientific DB-WAX megabore capillary column (30m x 0.53mm I.D. x 10μm film
thickness) was used for separation of different species. The GC method parameters were list in
Table 3-1.
A solution of 1-butanol with a known amount of internal standard was prepared a priori and used
for analysis. 1,4-butanediol was chosen as the internal standard since it is not one of the product
species and it exhibits similar properties to the components because it contains two hydroxyl
groups. An internal standard solution was prepared by adding 5g of 1,4-butanediol into 1L of 1-
butanol. The standards were purchased from Sigmal Aldridge Co. Canada. Before the
experimental samples were injected into the GC, a calibration for each sample standard was carried
out. The samples were prepared for analysis by adding around 120 mg of product sample to 1 mL
of prepared solution in a 2 mL glass vial. A 1 μL portion of the sample was injected into the
column. Fig. 3-3 depicts of chromatogram of one calibration standard with all possible products,
the species in an unknown sample can be determined based on the retention time of standards as
listed in Table 3-2.
Using the standard calibration curves that were prepared for all the components, the integrated
areas were converted to weight percentages for each component present in the sample. For each
data point, the theoretical selectivity of products was calculated.
31
Table 3-1 Detailed GC method
Inlet
Volume Injected 1 μL
Inlet Temperautre 300 ºC
Carrier Gas He
Inlet Pressure 5 psi
Total Flow 100 mL/min
Oven Temperature Profile
Initial Temperautre 100 ºC
Hold 2 min
Ramp1 10ºC /min to 133 ºC
Ramp2 1ºC /min to 143 ºC
Ramp3 10ºC /min to 200 ºC
Hold 15 min
FID Detector
Detector Temperautre 300 ºC
H2 Flow 40 mL/min
Air Flow 450 mL/min
Makeup Gas He
Makeup Flow 45 mL/min
A multiple-point internal standard method was used for the GC calibration. 6 calibration standards
which contained different amounts of each product species (50mg, 100mg, 150mg, 200mg, 250mg,
600mg) in 5mL of internal standard solutions were prepared for analysis. Then the response factor
of each component can be calculated using Equation 3-1. The calibrated response factor of each
species is listed in Table 3-2 and the calibration curves are shown in Appendix B.
32
Figure 3-3 A typical chromatogram of a GC calibration standard
.... SI
ii
SI
i
A
Ak
m
m Equation 3-1
where,
mi, Ai -- mass and area of each species respectively
mI.S., AI.S. -- mass and area of internal standard respectively
ki -- response factor of each species
Table 3-2 Retention Time and Response Factor for Each Compound
Compound 1-PO 1-Butanol Acetol 1,2-PD EG 1,3-PD 1,4-Butanediol GL
Retention
Time (min) 2.129 2.788 4.57 9.165 10.09 15.61 22.35 32.23
Response
Factor 0.791 - 1.518 1.242 1.668 1.215 1.0 1.645
Equation 3-2 was used to calculate the mass of each species in the sample. The glycerol conversion,
1-PO selectivity and yield of each product were calculated on a carbon basis from Equation 3-3 to
Equation 3-6.
Equation 3-2
33
..
..
SI
iiSIi
A
Akmm
Equation 3-3
remainglycerolofmoleproductbasedcarbonallofmole
productbasedcarbonallofmoleconversionGlycerol
________
______
Equation 3-4
productbasedcarbonallofmole
POofmoleyselectivitPO
_____
_1____1
Equation 3-5
productbasedcarbonallofmole
PDofmoleyselectivitPD
_____
_13____13
Equation 3-6
%100*________
___%
remainglycerolofmoleproductbasedcarbonallofmole
iproductofmoleYield i
3.5 Methods and Procedures for Catalyst Characterization Techniques
In order to study the physicochemical properties such as surface area, structure and acidity of the
catalysts and the relationship between the catalyst structures and catalytic activity to understand
the performance of the catalyst, some catalyst characterization experiments were carried out. The
different techniques used included: temperature programmed desorption (TPD), H2 Temperature
Programmed Reduction (TPR), powder X-ray diffraction (XRD), BET surface area analyis,
Thermal Gravimetric Analysis (TGA) and Fourier Transformed Infrared (FTIR) spectroscopy. In
this section, the methods and procedures for the catalyst characterization techniques are briefly
introduced.
34
3.5.1 AmmoniaTemperature Programmed Desorption (NH3-TPD)
NH3 Temperature programmed desoption is one of the most widely used and flexible techniques
for determining the amount and strength of acid sites of the catalysts due to the simplicity of the
technique. Determining the quantity and strength of the acid sites on the catalyst surface is crucial
to understanding and predicting the performance of a catalyst.
Preparation: Samples are usually degassed at 100°C for one hour in flowing helium/argon to
remove water vapor and to avoid pore damage from steaming which may alter the structure of the
support. The samples are then temperature programmed to a certain temperature and held at that
temperature for sometime to remove strongly bound species and activate the sample. Finally the
sample is cooled to 120°C in a stream of flowing helium/argon
Adsorption: The sample is saturated with the basic probe at 120°C; this temperature is used to
minimize physisorption of the ammonia. For ammonia, two techniques are available to saturate
the sample: pulsing the ammonia using the loop or continuously flowing ammonia. Pulsing the
ammonia allows the user to compare the quantity of ammonia adsorbed (via pulse adsorption) to
the quantity desorbed for the subsequent TPD. After saturation with ammonia, the sample is
purged for a minimum of one hour under a flow of helium to remove any of the physisorbed probe.
Desorption: The TPD is easily performed by ramping the sample temperature at 10°C/minute to a
given temperature. It is a good rule of thumb that the end temperature during the TPD should not
exceed the maximum temperature used in the preparation of the sample. Exceeding the maximum
preparation temperature may liberate additional species from the solid unrelated to the probe
molecule and cause spurious results. During the TPD of ammonia, the built-in thermal conductivity
detector (TCD) will monitor the concentration of the desorbed species. For the reactive probes
(propyl amines), a mass spectrometer is required to quantify the density of acid sites. For these
probes, several species may be desorbing simultaneously: ammonia.
NH3 Temperature programmed desoption was used to determine the amount and strength of acid
sites of the catalysts. Lower temperature desorption corresponds to weak acid sites and higher
tempereture to medium, strong acid sites. The catalyst was saturated under a flow of ammonia
after which the temperature of the sample was gradually increased and the amount of ammonia
desorbed was recorded as a function of time. The temperature at which ammonia desorbs is
35
associated with a particular type of acid site. Altamira AMI-200 Catalyst Characterization System
was used for the TPD experiments. The catalyst powder was screened through a sieve to make
sure that the particles with a size between 250μm and 500μm were collected for the TPD analysis.
In a typical experiment, approximately 120mg of catalyst was weighed and placed in a quartz U-
tube reactor. The catalyst sample was packed in one side of the U-tube reactor on a quartz wool
bed that was made of a small amount of quartz wool placed on both ends of the catalyst sample.
The U-tube was then secured to the sample station and enclosed by a furnace integrated with a
thermocouple. Prior to the TPD studies, the catalyst sample was reduced under a flow of 5% H2
(balanced Argon) at a volumetric flow rate of 30ml/hr at 300°C for 1h. After reduction, the catalyst
was cooled down to 50°C and was saturated by passing 5% NH3 (balance Argon) at a flow rate of
30ml/min for 1h and subsequently flushed with an Argon flow (30ml/min) at 50oC for 1h to remove
the physisorbed ammonia. Then TPD analysis was carried out by heating the catalyst from ambient
temperature to 750°C at a heating rate of 10°C/min for NH3 desorption. After the catalyst TPD
experiment, 5 pulses of a known volume (i.e. the sample loop volume of 524.0 µL) of 5% NH3
(balance Argon) were injected directly into the TCD without passing through the U tube for
calibration; the number of moles of ammonia injected can be calculated from the ideal gas law.
The ammonia concentration in the effluent stream was monitored with a thermal conductivity
detector and the area under the peak was integrated using software to determine the amount of
desorbed ammonia. The flow diagram for this system is shown in Fig. 3-4.
Figure 3-4 Diagram of the Altamira AMI-200 Catalyst Characterization System
36
The number of moles of NH3 desorbed during desorption step can be calculated using Equation 3-
7 and Equation 3-8.
areancalibratiomean
NHmlValuenCalibratio
__
%16.5524.0_ 3
Equation 3-7
5.24_
__)/(
weightsample
valuencalibratioareaanalyticalgcatmoleUptake Equation 3-8
3.5.2 H2 Temperature Programmed Reduction (TPR)
Temperature-Programmed Reduction (TPR) was used to reveal the number of reducible species
present on the catalyst surface and the temperature at which the reduction of each species occurs.
The TPR analysis begins by flowing an analysis gas (typically hydrogen in an inert carrier gas
such as argon) through the sample, usually at ambient temperature. While the gas is flowing, the
temperature of the sample is increased linearly with time and the consumption of hydrogen by the
adsorption/reaction is monitored. Changes in the concentration of the gas mixture downstream
from the reaction cell are determined. This information yields the volume of hydrogen uptake. In
this research, TPR experiments have been carried out to determine the appropriate reduction
temperature for each catalyst. The catalyst was loaded and reduced as described in section 3.4.1
for NH3-TPD. In a typical experiment, approximately 60mg of catalyst was weighed and placed
in a quartz U-tube reactor. The catalyst is reduced while the temperature is increased to find the
optimum reduction temperature. The catalyst was firstly heated to 200°C and kept at 200°C for 60
minutes under 30ml/min Argon flow to remove all the moisture and other species absorbed on the
catalyst surface. Then the catalyst was heated under 30ml/min 5% H2 balanced with Argon at a
heating rate of 5°C/min until 900°C and then the temperature was held at 900°C for 15 minutes.
3.5.3 Brunauer Emmett Teller (BET) Surface Area
The BET technique is a common technique used to measure the specific surface area of a material
by adsorbing gas molecules on a solid surface. The concept of the BET theory is an extension of
the Langmuir adsorption theory from monolayer to multilayer adsorption. Adsorption is the
phenomenon of gas molecules sticking to the surface of a solid. The concentrations of gas
37
(adsorbate) will be different on the solid (adsorbent) under different conditions, and this effect can
be used to determine the area of solid materials.
In a gas sorption experiment, the material is first heated and degassed by vacuum or inert gas
purging in order to remove any contaminants, volatile organics. A controlled amount of inert gas
such as nitrogen (N2), argon (Ar), or krypton (Kr) is then introduced, which adsorbs on the surface
of the material. The sample is placed under vacuum at a low temperature, usually at the boiling
point of liquid nitrogen (-195.6°C). The sample is then subjected to a wide range of pressures. The
amount of gas molecules adsorbed will vary as the pressure of the gas is varied. When the quantity
of adsorbate on a surface is measured over a wide range of relative pressures at constant
temperature, the result is an adsorption isotherm. The resulting adsorption isotherm is analyzed
according to the BET method. The BET surface area can be calculated via equation 3-9:
𝑃
𝑛(𝑃0−𝑃)=
1
𝑐𝑛𝑚+
𝑐−1
𝑐𝑛𝑚∗
𝑃
𝑃0 Equation 3-9
where P, P0, c, n, nm are the adsorption pressure, the saturation pressure, a constant, the amount
adsorbed (weight of adsorbate) at the relative pressure P/P0, and the monolayer capacity (weight
of adsorbate constituting a monolayer of surface coverage), respectively [114]. Through the slope
and intercept of a plot of P/[n(P0-P)] against (P/P0), nm can be determined. The cross-sectional area
(ACS) occupied by one N2 adsorbate molecule is 16.2Å2. The BET surface area can be calculated
using equation 3-10:
𝐴 = 𝐴𝐶𝑆∗𝑛𝑚∗𝑁𝐴
𝑀𝑁2
Equation 3-10
Where, NA is the Avogadro’s number, and MN2 is the molar mass of N2, 28g mol-1. The specific
surface area is then calculated by dividing the area A by the sample weight.
In this thesis research, the BET surface area was determined using a Micromeritics Gemini VII
instrument with nitrogen physisorption at 77 K, taking 0.162 nm2 as the cross sectional area for
di-nitrogen. The analysis was carried out on calcined catalyst. Catalyst samples were desgassed
under nitrogen at 300°C in 3 hours to desorb the moisture on the catalyst surface then cooled down
to room temperature and weighed before proceeding BET analysis.
38
3.5.4 Thermal Gravimetric Analysis (TGA)
Thermo Gravimetric Analysis (TGA), an analytic technique that measures the weight loss (or
weight gain) of a material against temperature or time technique, can provide information on the
thermal stability of the compound in the solid state and the amount of crystal waters present. TGA is
an analytic technique that measures the weight loss (or weight gain) of a material against temperature
or time. As materials are heated, they can lose weight from drying, evaporation and decomposition.
Some materials can gain weight by reacting with the air.
A TGA Q500 was used for TGA thermal analysis. The panel was filled with around 10mg of
catalyst sample. Then the sample was heated under 100ml/min air flow from room temperature to
900 ºC.
3.5.5 X-Ray Diffraction (XRD)
XRD was used to study the composition of the catalysts. It is also useful to determine if the material
under investigation was crystalline or amorphous. The calcined catalyst was attacked by X-rays at
various angles. Intensity of the reflected X-rays depends on the relative arrangement of atoms in
the crystal. The angle of X-rays reflected from crystal depends on the dimensional characteristics
of the lattice. Each material has a unique X-ray diffraction pattern.
The XRD patterns were obtained on a Bruker D8 Focus model. The configuration included power
of 40 kV, current intensity, 1.0 mm divergence slit, 1.0 mm anti-scattering slit, 0.1 mm detector
slit and 0.6 mm receiving slit. Cu kα radiation wave length was set to 1.54 Å; the 2θ angle was set
at 20o-80o with a ramp 0.02o per minute. The catalyst was crushed well to produce fine particles
before doing experiment.
The average crystallite size was calculated using the Scherrer equation. If there is no
inhomogeneous strain, the crystallite size D can be estimated from the peak widthby the Scherrer’s
formula:
D = kλ/B(2θ)cosθ
where λ is the X-ray wavelength, B is the full width of height maximum of a diffraction peak, θ is
the diffraction angle, and k is the Scherrer constant which is of the order unity for usual crystal.
39
3.5.6 Fourier transform infrared spectroscopy (FTIR)
The use of FTIR as a characterization technique is based on the vibrational frequencies of the
chemical bonds. The vibrational motions of the chemical bonds in a material have frequencies in
the infrared regime. In the infrared technique, the intensity of a beam of infrared radiation is
measured before (IO) and after (I) its interaction with the sample as a function of light frequency.
The plot of I/IO versus frequency is the “infrared spectrum”. By using FTIR, information about
the identities, surrounding environments and concentrations of the chemical bonds in the material
can be obtained [115]. FTIR spectra are capable in revealing information about the functional
group present within a molecule. Infrared spectroscopy FTIR can then supply a “fingerprint” of
the compound made showing the typical M-O bond vibration peaks, where M can be the addenda
or the heteroatom. FTIR spectroscopy was performed in order to observe any significant changes
in the chemical structures of the Keggin anion of the catalyst.
FTIR analyses of the catalysts were recorded using a Nicolet 6700 FTIR spectrum from Thermo
Electron Corporation using a KBr disc technique and working with resolution of 4 cm-1 in the
middle range. The spectra were recorded with 32 scans between 400 and 4400 cm-1 with a
resolution of 4cm-1. For the FTIR analysis, the samples were analyzed after dilution in KBr as
follows. Approximately 5mg (2.5wt.%) sample is well mixed into 200 mg fine alkali halide (here
KBr is used) powder and then finely ground and put into a pellet-forming die. A force of
approximately 10 tons is applied under a vacuum of several mm Hg for several minutes to form
transparent pellets. Before forming the KBr powder into pellets, it was pulverized to 200 mesh
max. and then dried at approximately 110 °C for three hours. When performing measurements, the
background was measured with an empty pellet holder inserted into the sample chamber. The
chemical bonds present in the structure of the materials were identified by this analysis technique.
40
Chapter Four
Conversion of glycerol to lower alcohols using 10Ni/30HSiW/Al2O3
catalyst in a Stainless Steel batch reactor
Much work has been done towards the hydrogenolysis of glycerol to 1,3-PD and 1,2-PD, however,
routes to lower alcohols, such as 1-PO have been less frequently reported.A literature review
showed that various heterogeneous systems including Rh, Ru, Pt, PtRu, Cu systems and Raney Ni
are studied for the hydrogenlyis of glycerol to lower alcohols. Surprisingly, the use of supported
Ni systems as catalysts towards the chemical transformation of glycerol, especially towards the
formation of lower alcohols, has appeared less frequently in the literature. Therefore the main
purpose of this chapter was the production of lower alcohols, primarily 1,3-PD and 1-PO from
glycerol using 10Ni/30HSiW/Al2O3 catalysts in a stainless steel batch reactor.
In this chapter, the effect of metals of Pt, Pd, Ni and Cu and the effect of Cs+ substitution of H+ on
the activity and selectivity of the catalyst for the hydrogenolysis of glycerol in a batch reactor was
investigested. The catalysts were synthesized in our lab via an impregnation method, and then
crushed and sieved to less than 250μm before testing to minimize internal mass transfer effects.
Prior to each experiment, the catalyst was reduced in a quartz tubular reactor at 350oC for 5h.
Reactions were performed in a 300ml Parr Instrument 4182 Series constructed of stainless steel
T316. After sealing the reactor the reaction mixture was purged with N2 gas several times and then
with H2 gas while stirring gently at 50 RPM to remove all the oxygen from the headspace and any
dissolved oxygen in the solvent. The reactor was then pressurized to the target pressure and heated
to the required temperature. When the reactor had just reached the required temperature, the
stirring speed was increased to 700 RPM at which point the first sample at 0 hour was taken. The
progress of the reaction was followed by sampling at regular intervals during the reaction. The
reactor was maintained at 240oC during the reaction.
4.1. Effect of metals on the hydrogenolysis of glycerol
Since hydrogenolysis requires hydrogen for hydrogenation, the hydrogenolysis catalyst must have
an ability to activate hydrogen molecules. In this section different metals supported on
30HSiW/Al2O3 catalysts were studied for the hydrogenolysis of glycerol. Noble metals are well
41
known to be able to activate hydrogen molecules and are widely used as hydrogenation catalysts.
Pt supported HPAs catalyst is one of the most active supported catalysts for the hydrogenolysis of
glycerol and has been intensively studied by many researchers for the upgrading of glycerol to
other value-added chemicals [77-79, 86]. Although research has been carried out towards the
hydrogenolysis of glycerol to 1,2-PD and 1,3-PD, hardly any work has been reported on the one-
pot direct conversion of glycerol to 1-PO. For the conversion of glycerol to 1-PO, noble metals
such as Rh, Ru, Pt are often used but the selelctivity to 1-PO can reach only as high as of 80%.
[45, 78, 116]. A non-noble metal such as Cu has also been intensively investigated for the
upgrading of glycerol [63, 105, 117] but the catalysts does not show their effectiveness toward
selectivity of 1-PO. Ni-based catalysts show acceptable activities and selectivities at moderate
costs of manufacturing, especially as compared to the costs associated with catalysts based on
noble metals. Ni-based catalysts can also have high catalytic activity and selectivity for the
hydrogenation of aldehydes especially in converting 3-HPA (3-hydroxypropionaldehyde) to 1,3-
PD [112, 118-121]. However, to date Ni supported catalysts have not been reported for the one-
pot hydrogenolysis of glycerol to produce 1-PO. The production of 1-PO either was carried out
under high temperature (320oC), high pressure of H2 (6MPAa) in fix-bed reactor or the catalyst
was packed in a sequential two-layer catalysts [122] and the selectivity of 1-PO is still low.
In the present section, bi-functional catalysts were synthesized with different metals (i.e. Ni, Pd,
Pt, Cu) and HSiW supported on Al2O3 as bifunctional catalysts by a sequential impregnation
method for the one-pot hydrogenolysis of glycerol to lower alcohols, in particular, to 1-PO. The
catalysts were characterized using XRD and NH3-TPD techniques. A comparison of the reactivity
and the product selectivity of the Ni catalyst with the Pd, Pt and Cu catalysts were carried out. Rate
constants for the conversion of glycerol, 1,2-PD and 1,3-PD, 1-PO was determined for a
10Ni/30HSiW/Al2O3 catalyst and a reaction pathway was proposed.
Experiment condition
The effect of metals on the overall reaction is studied by carrying out the hydrogenlolysis of
glycerol using different metals loading under the same reaction condition. Prior to each
experiment, the catalyst was reduced in a quartz tubular reactor at 350oC. The experiment was
performed at 240oC, 700RPM under 880 H2 pressure using 4g of metal supported 30HSiW/Al2O3
42
catalyst, 30g of glycerol, 70g deionized water in 8 hours. The properties of the prepared catalysts
were characterized using NH3-TPD, XRD techniques.
Results and discussion
Characterization of catalysts
The catalysts were characterized by XRD and NH3-TPD techniques to study the relationship
between catalytic activity and catalyst properties in particular the acid concentration of the
catalysts.
XRD patterns of all catalysts are shown in Fig. 4-1 and 4-2. It can be seen that the XRD patterns
are similar for all the catalyst with 1 wt% Pt, 1 wt% Pd, 1 wt% Ni supported on 30HSiW/Al2O3.
In all the samples, no diffraction lines due to Ni, Pd and Pt were observed. Hence the XRD patterns
suggest that at a low level of metal loading of 1 wt% that the metal oxide species is present in a
highly dispersed amorphous state. In Fig. 4-2, the XRD patterns show that when Ni loading
increases from 1 wt% to 10 wt%, the diffraction peak of NiO was observed. Thus the nickel oxide
is present in a highly dispersed amorphous state at 1wt % Ni in the sample and as a crystalline NiO
phase at a 10 wt% Ni loading.
Figure 4-1 XRD patterns of 1 wt% metal
loading on HSiW/Al2O3 catalyst
Figure 4-2 XRD patterns of 1wt% and 10 wt%
Ni loading on HSiW/Al2O3 catalyst
The NH3-TPD measurements were carried out to compare the acidity of different metal supported
30HSiW/Al2O3. The NH3-TPD profiles are shown in Fig. 4-3 and 4-4. The TPD data was
43
deconvoluted into 3 peaks (namely weak, medium and strong acid sites) using a Gaussian fitting
method. The results are shown in Table 4-1.
Figure 4-3 NH3-TPD patterns of different
metals (Ni, Pd, Pt) loading on 30HSiW/Al2O3
catalyst
Figure 4-4 NH3-TPD patterns of 1 wt % and 10
wt% Ni supported 30HSiW/Al2O3 catalyst
Table 4-1 Total acidity of catalysts
Catalyst
Weak acid site
mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid
site mmol/g
/(Temp.)
Total acid
amount,
mmol/g
30HSiW/Al2O3 0.149/ (155oC) 0.379/ (243oC) 0.461/ (439oC) 0.989
1Ni//30HSiW/Al2O3 0.228/ (167oC) 0.308/ (259oC) 0.330/ (460oC) 0.866
1Pd/30HSiW/Al2O3 0.205/ (172oC) 0.242/ (254oC) 0.425/ (442oC) 0.873
1Pt/30HSiW/Al2O3 0.235/ (178oC) 0.194/ (281oC) 0.441/ (428oC) 0.869
10Ni/30HSiW/Al2O3 0.124/ (162oC) 0.233/ (246oC) 0.215/ (427oC) 0.572
10Cu/30HSiW/Al2O3 0.108/ (162oC) 0.201/ (230oC) 0.347/ (345oC) 0.657
As it can be seen from Table 4-1, 1wt% metal loading decreases the total acidity of the
30HSiW/Al2O3 catalyst by approximately 10%. A decrease in acidity may possibly be due to the
covering of acid sites by metal, or from the direct anchoring of metals on proton sites, and or from
blockage of the access to the acid sides by metal particles. However, the total acidity of the 1wt %
of Ni, Pd or Pt supported 30HSiW/Al2O3 catalysts is quite similar. Although the total acidity of
44
the catalyst does not depend on the type of metal loading, the distribution of the strength and
amount of the acid sites appear to be dependent on the type of metal, however the variation is not
very significant.
Fig. 4-4 shows that an increase in Ni loading from 1wt% to 10 wt% leads to a significant decrease
in the acidity of the catalyst. This suggests the possibility in covering the acid sites by adding
metal or direct anchoring on proton sites, and from blockage of acid channels by metal particles.
The addition of 10 wt% Cu causes a significant reduction in the strength of the acid sites of the
catalyst. As can be seen from Table 4-1, the amount of weak and medium acid sites diminishes,
and interestingly the amount of strong acid sites increases but the peak shifts to a lower temperature
(345ᵒC compared with 427ᵒC for the catalyst with 10% Ni) indicating a lower acid strength.
Activity test results
To establish the role played by the metallic sites of the catalyst in the hydrogenolysis of glycerol,
a series of metal (Pt, Pd, Ni and Cu) supported 30HSiW/Al2O3 catalysts were prepared and used
for the conversion of an aqueous solution of a 30wt. % glycerol initial concentration under an
initial H2 pressure of 880PSI at room temperature . The main products observed in the liquid phase
were: acetol, 1,2-PD, 1,3-PD, acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products
(OP) such as methanol, ethanol were also obtained. In addition, some other products were detected
but not identified (UIP).
The conversion and product selectivity data for the catalysts are shown in Table 4-2. The first set
of experiments were performed with 1% metal loading of Ni, Pd and Pt onto 30HSiW/Al2O3 and
compared with the parent catalyst 30HSiW/Al2O3. The data shows that these metals affect both
the glycerol conversion and product distribution. It is interesting to observe that the addition of Pt,
Pd and Ni increased the glycerol conversion which could be attributed to the higher hydrogenation
activity of these metals. The dehydration of glycerol to form acetol or 3-HPA shown in Scheme 4-
1 is reversible. Hydrogenation of the intermediates formed from the dehydration of glycerol will
shift the equilibrium to 1,2-PD or 1,3-PD and increases the conversion of glycerol. Besides
differences in glycerol conversion, the product distribution of the parent catalyst is also quite
different than those with added Ni, Pt, Pd. The parent catalyst yields a higher selectivity to acrolein
but no 1,3-PD is detected. Dehydration of the secondary alcohol group in glycerol will produce 3-
45
HPA which could either be further dehydrated to form acrolein or hydrogenated to produce 1,3-
PD. Since the parent catalyst is the most acidic catalyst in this study but deficient in effective
hydrogenation sites, hence acrolein was obtained in high selectivity and interestingly no 1,3-PD
was detected. Addition of 1 wt% of Ni, Pd, Pt significantly increases the conversion of glycerol
due to the hydrogenation of the dehydration intermediates acetol or 3-HPA to produce 1,2-PD or
1,3-PD respectively. Further hydrogenolysis of 1,2-PD or 1,3-PD produces 1-PO. While addition
of 1 wt% Pt to the parent catalyst increases glycerol conversion with a higher selectivity to 1,3-PD
and 1-PO, it is interesting to observe addition of 1 wt% Ni also promotes the hydrogenolysis of
glycerol to 1-PO with activity and selectivity similar to that of Pt and Pd.
The nominal weight loading of Ni in Ni/30HSiW/Al2O3 was increased to 10wt% in an attempt to
promote the hydrogenolysis and conversion of glycerol. The reactivity was also compared with a
catalyst with 10wt% Cu loading on 30HSiW/Al2O3 under the same reaction conditions. As can be
observed from Table 4-2, by increasing the Ni loading from 1 wt % to 10 wt% Ni there was a
decrease in the conversion of glycerol; however, it increases the selectivity to 1,2 PD and 1-PO
and reduces the selectivity of the unidentified products (UIP). A higher Ni loading apparently
increases the selectivity to lower alcohols possibly due to the increased hydrogenation activity. As
discuss above, a higher loading of Ni decreases the strong acidic sites of the catalyst (Fig. 4-4 and
Table 4-1) which caused the decrease in the conversion of glycerol as the first step for glycerol
conversion is the acid catalyzed dehydration. Since Ni, an inexpensive transition metal has activity
comparable to Pt, the activity of another inexpensive transition metal was also investigated.
Surprisingly, the catalytic activity of the 10 wt% Cu loaded catalyst decreased remarkably. The
selectivity to lower alcohols such as 1,2-PD and 1-PO is low; also no 1,3-PD or EG were detected
using a Cu supported 30HSiW/Al2O3 catalyst. Interestingly acrolein was obtained. The product
selectivity suggests that Cu is not effective for hydrogenation under this reaction condition. It is
worth noting that the strength of the acid sites of the Cu loaded catalyst is much less that the other
metals (Fig. 4-4, Table 4-1). Whilst the strength of acid sites affects dehydration which is reflected
in lower glycerol conversion; the lower selectivity to the desired products is attributed to the lower
hydrogenation activity of Cu compared to Ni, Pd and Pt.
46
Table 4-2 Effect of metal loading on catalytic performance
Reaction condition: M/30HSiW/Al2O3 catalyst (M: Pt, Pd, Ni, Cu), 240oC, 880PSI initial H2, 30g
of glycerol (30wt%), 70g of DI water, 4g catalyst, 8 hours. U.I.P.: unidentified products (*: one
heavy product, **: some light and heavy products)
In order to elucidate the reaction pathway for glycerol conversion, the hydrogenolysis of 1,2-PD,
1,3-PD, 1-PO over 10Ni/30HSiW/Al2O3 was also evaluated under conditions similar to that of
glycerol and the results are presented in Table 4-3. The pseudo first order rate constants for the
conversion of glycerol, 1,2-PD, 1,3-PD and 1-PO under the same reaction conditions were
calculated and are presented in Fig. 4-5. As can be seen the conversion of 1,3-PD was lower than
that of glycerol and 1,2-PD, the pseudo first order rate constants for the conversion of 1,2-PD and
1,3-PD shows the rate constants for the conversion of 1,2-PD is 15 times faster than for 1,3-PD.
Therefore, 1-PO is mainly produced from 1,2-PD with a high conversion of 1,2-PD and high
selectivity to 1-PO. Since the conversion of 1-PO was much lower than that of 1,2-PD and 1,3-
PD, it can be assumed that 1-PO is stable under the reaction condition and becomes the final
product in the hydrogenolysis of glycerol using 10Ni/30HSiW/Al2O3. It is interesting to note that
ethylene glycol was obtained in the glycerol hydrogenolysis, however, it was not detected in the
hydrogenolysis of 1,2-PD and 1,3-PD suggesting that ethylene glycol was produced directly from
glycerol by a C–C bond cleavage reaction. In the reaction of glycerol and 1,2-PD, ethanol was
observed which can be formed via sequential hydrogenolysis of ethylene glycol or decomposition
of 1,2-PD.
Entry Catalyst Conv
mol%
Selectivity, mol%
1,3PD 1,2PD Ac EG 1-PO Acr MeOH EtOH UIP
1 30HSiW/Al2O3 14.5 0.0 0.0 6.0 0.0 30.5 19.7 5.3 9.1 29.4**
2 1Ni/30HSiW/Al2O3 39.2 3.0 4.1 3.3 0.0 54.7 3.4 3.4 2.9 25.2*
3 1Pd/30HSiW/Al2O3 34.1 5.4 4.7 4.1 0.0 51.4 1.9 4.1 8.7 21.7*
4 1Pt/30HSiW/Al2O3 45.3 10.5 5.7 2.5 1.8 59.2 1.9 0.0 5.1 13.3*
5 10Ni/30HSiW/Al2O3 33.2 7.9 10.5 3.8 4.4 60.7 1.5 1.8 4.8 4.6*
6 10Cu/30HSiW/Al2O3 18.0 0.0 4.2 5.3 0.0 31 12.6 0.0 8.2 42.9**
47
Table 4-3 The hydrogenolysis of 1,2-PD, 1,3-PD and 1-PO
Reactant Glycerol 1,2PD 1,3PD 1-PO
Conversion,
mol% 33.2 98.1 26.4 8.5
Selectivity, mol%
Acetol 3.8 0.6 0.0 0.0
1,2PD 7.9 - 0.0 0.0
1,3PD 10.5 0.0 - 0.0
1-PO 60.7 90.8 77.4 -
EG 4.4 0.0 0.0 0.0
MeOH 1.8 0.0 0.0 0.0
EtOH 4.8 2.1 15.0 20.7
Acr 1.5 0.0 0.8 0.0
Propanal 0.0 4.5 0.0 79.3
UIP 4.6 2.6 6.8 0.0
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240oC, 880PSI initial H2, 30g of glycerol
(30wt%), 70g of DI water, 4g catalyst, 8 hours
Figure 4-5 Pseudo-first-order rate constants for the 10Ni/30HSiW/Al2O3 catalysts using different
starting material. Reaction condition: 240ºC, 880PSI H2, 700RPM, 4g catalyst, 30g of glycerol
(30wt%), 70g of DI water.
It is interesting to note that the rate constant for the conversion of 1,2-PD is the highest, followed
by glycerol. The conversion of 1,3-PD is slower than the glycerol conversion while the conversion
48
of 1-PO is the slowest. These rate constants provide important formation on the proposed reaction
pathway for glycerol hydrogenolysis and also the product selectivity.
Summary
Ni, Pd, and Pt promote the activity of the 30HSiW/Al2O3 supported catalyst for the conversion of
glycerol to higher value chemicals such as 1,3-PD, 1,2-PD and in particular 1-PO. Among these
metals, Pt is the best promoter for the production of 1,3-PD, a very high value intermediate for
valuable polymers. Although it is reported that Cu possesses good hydrogenation activity that is
comparable with Ni, Cu does not show activity for the production of 1,3-PD under this reaction
conditions. Interestingly Ni, a much cheaper metal, has fairly comparable reactivity to Pt.
The much lower price of Ni compared to Pt is very attractive for a new green process development
for the conversion of glycerol to sustainable higher value products. To obtain a desired product
selectively, the control of reaction conditions and catalyst properties such as acid strength, the
amount of appropriate acid sites and metal hydrogenation activity will be needed. Optimization
of the catalyst preparation techniques and a balance of Ni and HiSiW loading on various supports
could lead to high yields of value-added chemicals from glycerol. Due to the inexpensive Ni-based
catalyst and the high selectivity, an economical production of green and sustainable 1-PO from
glycerol hydrogenolysis may be feasible for future commercial development. 1-PO is mainly
produced from 1,2-PD with a high conversion of 1,2-PD and high selectivity to 1-PO and 1-PO is
stable under the reaction condition and is assumed as the final product in the hydrogenolysis of
glycerol using 10Ni/30HSiW/Al2O3.
4.2 Effect of Cs+ on activity of 10Ni/30HSiW/Al2O3 catalyst
In this section, effect of Cs+ exchanged H+ in the 10Ni30HSiW/Al2O3 catalyst was investigated
for hydrogenolysis of glycerol.
Although HPAs are useful solid catalysts, the specific surface area of these solid materials is very
low making low dispersion, agglomeration or leaching of HPAs still a crucial limitation. In order
to increase the efficiency of HPA-catalyzed processes these disadvantages have to be overcome.
One of the possible solutions is synthesizing salts of them since the protons in Keggin HPAs can
be readily exchanged, totally or partially, by different cations without affecting the primary Keggin
49
structure of the heteropoly anion. It is reported that the presence of counter cations such as Cs+,
Rb+, K+ in replacement of protons can modify the physicochemical properties (reduces water
solubility and simultaneously increases specific surface area [123] of heteropolyacids ) therefore
the method to control these properties can be established by exchange of protons by various
alkaline metals in different concentrations [85]. In this way, a partial neutralization of HPA’s with
these cations is achieved and insoluble salts of HPA’s are obtained that also contribute to improve
their catalytic activity by increasing the HPA dispersion [124]. It is evident that the protons in the
heteropolyacids are the source of catalyst activity because most of the completely cation
exchanged salts were inactive in acid-base catalysis. It has been reported that acidic HSiW
promotes the condensation of formaldehyde and methyl formate to methyl glycolate and methyl
methoxy acetate whereas completely cation exchanged compounds are inactive [125]. Haber et al.
[126] studied the synthesis of metal salts of HPA’s in pure form and also supported them on silica
and tested them in dehydration of ethanol and hydration of ethylene. It was reported that the
structure of salts of heteropolyacids were affected by the type of counter cation present. Salts with
small cations like Fe, Co, Ni or Na resembled the parent HPA, as they were water soluble,
nonporous and had low surface areas. On the other hand, salts of HPA with large monovalent
cations such as NH4+, K+, and Cs+ were water insoluble, had rigid micro/mesoporous tertiary
structure and had high surface areas [126, 127]. Kozhevnikov stated that when in the form of salts,
thermal stability of heteropolyacids is higher than their acid forms [128].
The most-studied insoluble salt of HPAs is Cs salt that is a well-known acidic catalyst in which
the residual protons are more acidic than the homogeneous acid catalysts (e.g. H2SO4). Partial
substitution of protons of HPAs by Cs+ results in a higher thermal stability. When in the form of
salts, thermal stability of heteropolyacids is higher than their acid forms. It is reported that
properties of HPAs such as solubility, crystalline structure, porosity, surface area, amount of water
of crystallization and thermal stability are sensitive to the amount of Cs+ substituted [124,
129,130]. Alkaline substituted of Cs+ HPAs catalysts have also attracted much attention due to
their high surface area and tunable porosity which enable them for the use in dehydration reaction.
[131-133]. Okuhara et al. [134] concluded that the pore size of the acidic Cs salts (CsxH3-xPW12040)
was controlled by the Cs+ content, the shape selective catalysis was observed and the acidic Cs
salts were strongly acidic and when compared to the zeolites SO42-/ZrO2, they were more
catalytically active for decomposition of esters and alkylation in liquid-solid reaction system. In
50
1995, Essayem et. al. confirmed that the Cs salts of H3PW12040 exhibit a much higher surface area
than their acid analog and the enhancement of the surface area results obviously in a strong increase
in specific catalytic activity in the conversion of methanol to dimethyl ether. The amount of acidity
and the acid strength depends differently on the Cs content [135]. In 1998 Bardin et al.[136] tested
the heteropolyacid H3PW12040 and its Cs salts CsxH3-xPW12040 (x = 1, 2, 2:5, 3) for isomerization
and it was found that incorporation of Cs into the heteropolyacid decreased the acidic protons
available for catalysis, increased the specific surface area, and increased the thermal stability. In
2013 E. Rafiee et. al. investigated the activity of CsxH3-xPW12040 (X = 0, 1, 2, 2.5 and 3) catalysts
in the synthesis of β-ketoenol ethers [137]. It was reported that activity; acidity, solubility and
consequently, recoverability of these catalysts are related to Cs content. Shaimaa M. Ibrahim also
mentioned in his work that the catalytic activity and selectivity towards dehydration and
dimerization processes of the catalysts are much affected by the number of substituted acid protons
by alkali metal. The surface area of the supported Cs or K salts of HPW increased progressively
by increasing the number of protons substituted by Cs+ or K+ which resulted to an increase in the
catalytic activity [138]. Narasimharao et. al. investigated the relations in structure–activity and Cs-
doped heteropolyacids catalysts for biodiesel production [139]. It was found that the total acid site
density decreases with Cs+ exchange. All samples with x > 1 are resistant to leaching and can be
recycled without major loss of activity in particular Cs2.3H0.7PW12O40 can be used without loss of
activity or selectivity. Pesaresi et. al. [140] used Cs-doped H4SiW12O40 catalysts for biodiesel
applications and it is found that low loadings ≤0.8 Cs per Keggin, (trans) esterification activity
arises from homogeneous contributions. However, higher degrees of substitution result in entirely
heterogeneous catalysis, with rates proportional to the density of accessible acid sites present
within mesopores. In 2015 Sujiao et. al. [141] studied CsxH3+
n-xPMo12-nVnO40 catalysts (n=0, 1, 2,
x=0.5-3.0) in the direct hydroxylation of benzene reaction. It is found that the leaching of catalyst
decreases significantly with increasing the Cs content.
Although considerable research has studied the effect of Cs substituted HPAs catalyst to improve
the catalytic activity in reactions, there are only a few reports on the effect of Cs+ exchanged HPAs
catalyst for the glycerol conversion. Alhanash et. al. [85] demonstrated that the water-insoluble
Cs heteropoly salt, Cs2.5H0.5PW12O40, possessing strong Brønsted acid sites and high water
tolerance is an active catalyst for the dehydration of glycerol to acrolein. The catalyst exhibits high
initial activity, with a glycerol conversion of 100% at 98% acrolein selectivity. Recently, Atia et
51
al. [72] investigated a series of Li, K and Cs modified HSiW catalysts for glycerol dehydration
and found that addition of alkaline metals Li, K and Cs has greatly improved the desired acrolein
selectivity and activity. The incorporation of alkaline metals into HPAs helps to regulate to some
extent the dispersion of active species on the support surface, strengthen the water-tolerance and
simultaneously adjust the acidity, resulting in increased activity and stability, particularly in polar
water medium. In 2012 Haider et. al. [142] found that Cs-doped HSiW supported on a mixture of
theta and delta phases of alumina was stable for up to 90-h reaction time and gave a maximum
selectivity of 90% acrolein at 100% glycerol conversion. It’s suggested that the origin of the long-
term stability is related to the strength of the partially doped silicotungstic acid on the alumina
support. Doping with Cs maintains the Keggin structure of HSiW, resulting in long-term stability
and the high acrolein yield observed. The binding strength of the partially doped silicotungstic
acid on the alumina was found to be crucial to sustain the supported Keggin structure and hence
the acidity of the active sites resulting in a high acrolein yield. Zhu, et. al. reported that the addition
of Cs by ion exchange tunes the acidic properties of HSiW and hence could affect the catalytic
performance for glycerol hydrogenolysis [86].
From our previous work, it is reported that the 10Ni/30HSiW/Al2O3 catalyst is a potential
candidate for 1-PO production. It is therefore valuable to investigate the effect of Cs+ substitution
to improve the selectivity and stability of the HSiW supported catalysts and to control the acidic
properties for glycerol conversion. In the present work, we exchanged protons with the Cs ion for
the hydrogenolysis of glycerol to lower alcohols, in particular, to 1-PO. A series of different Cs+
content of Keggin-type HPAs 10Ni/30H4−xCsxSiW/Al2O3 (x=0-4) were prepared and the activity
test of catalysts for the hydrogenolysis of glycerol was carried out in a stainless steel batch reactor.
The catalysts were characterized using BET, FTIR, XRD and NH3-TPD techniques. The effect of
Cs+ exchanged H+ on the activity of Ni-free 30HSiW/Al2O3 (30CsxH4-xSiW/Al2O3) (x=0-4)
catalysts were also studied for comparison.
4.2.1 Experimental conditions
Catalyst preparation
The 10Ni30CsxH4-xSiW/Al2O3 (or 30CsxH4-xSiW/Al2O3) catalysts were prepared via ion
exchange. A set of cesium-exchanged HSiWs were prepared by an ion-exchange method with a
52
variation of cesium content. A known amount of cesium chloride (CsCl, Sigma-Aldrich) was
dissolved in distilled water then added to a desired amount of 10Ni30HSiW/Al2O3 (or
30HSiW/Al2O3 was added to this solution) and aged for 4 hours without mixing. After that, the
round bottle with the aged solution was evaporated on an oil bath at 70oC until the solvent
evaporated completely. Then the catalyst was dried in an oven at 110oC overnight. Finally, it was
calcined at 350oC for 5 h to yield the 10Ni30CsxH4-xSiW/Al2O3 (or 30CsxH4-xSiW/Al2O3). Before
carrying out an experiment the catalyst was reduced with hydrogen at 350oC for 5 hours.
Experimental condition
The effects of the different cesium (Cs+) content on catalytic performance was performed in a
300ml Stainless Steel Parr batch autoclave using 30g glycerol, 70g DI water, 580PSI Hydrogen at
240oC. 700 RPM and 4g of catalysts 10Ni/30CsxH4−xSiW/Al2O3 (x=0-4). The main products
observed in the liquid phase were: Acetol, 1,2-Propanediol (1,2-PD), 1,3-Propanediol (1,3-PD), 1-
Propanol (1-PO) and ethylene glycol (EG). Some other products such as methanol (MeOH),
ethanol (EtOH), acrolein (Acr) were also obtained and named as other products (O.P.). The
properties of the prepared catalysts were characterized using BET, TPD, XRD and FTIR
techniques.
Results and discussion
Characterization of catalysts
Acid properties of the catalyst with different Cs+ content were explored by NH3-TPD from 50 to
750◦C to determine the quantity of acid sites on the catalyst surface and the distribution of acid
strength of the catalyst in order, to find a comprehensive correlation between Cs+ content with
catalytic activity and acid property of the 10Ni/30HSiW/Al2O3 catalysts. Fig. 4-6 shows the
profiles of NH3-TPD desorption from the catalysts. As can be seen, all samples presented a broad
profile between 100 and 550◦C, revealing that the acid property and surface acid sites were widely
distributed and indicating the presence of different acid sites with different strengths. The TPD
data was then de-convoluted into 3 peaks (namely weak, medium and strong acid sites) using a
Gaussian fitting method and the results are shown in Table 4-4.
53
Table 4-4 showed that generally Cs+ exchanged H+ decreases the total acidity of the
10Ni/30HSiW/Al2O3 catalyst. When the Cs+ loading is less than 1, the acidity is very similar to
the parent catalyst with four protons , on further increase in Cs+ loading from 1 to 3 , the acidity
decreases almost linearly and gradually tails off at Cs+ loading of 4 when all the protons are
replaced nominally (Fig. 4-7). The exchange of Cs+ also causes a modification in the distribution
of the acid strength of the catalysts. It was found that the strength of medium acid sites was
significantly affected by adding Cs+. With a Cs+ content from 0 to 2, 3 peaks of weak, medium
and strong acid sites were observed, and with further increasing of Cs+ to 3 and 4, the medium acid
sites significantly diminished and only 2 peaks of weak and strong acid sites remained. It is noticed
that the exchange of 3 and 4 Cs+ resulted in a complete removal of medium acid sites but an
increase of the strength of strong acid site as the peak shifts to a higher temperature of 442oC. The
above results clearly showed that these catalysts possess different acid sites, while catalysts with
0Cs+, 1Cs+ and 2Cs+ have medium acid sites, catalysts with 3Cs+ and 4Cs+ do not. With an increase
of Cs+ content from 0 to 2, the acid strength of all acid sites (weak, medium and strong) of the
catalysts decreased gradually, and the desorbed ammonia peaks of catalysts with 0Cs+, 1Cs+ and
2Cs+ shift to lower temperature. It is noticed that there is a significant drop in medium acid sites
when 3 protons were substituted by 3Cs+ or all the 4 protons was totally substituted with 4Cs+
(the amount of medium acid site almost drop to nearly 0mmg/g respectively). These results
illustrated that Cs+ substitution decreases both the amount of acidity and the acid strength of the
catalysts. It is believed that Cs+ eliminates the acid sites of catalyst by replacing the proton source
and an inverse relationship (Table 4-7) is observed between Cs+ content and acid concentration on
the catalysts.
Surface area of 10Ni/30CsxH4−xSiW/Al2O3 (x=0-4) catalyst was determined by BET and presented
in Table 4-4. As can be seen the surface area of the 10Ni/30HSiW/Al2O3 catalyst increased with
the increasing of Cs+ content, which was similar to the reports in the literature [143] with an
exception of the catalyst with the full substitution of protons where the surface area significantly
decreases. This impact of Cs+ ions on surface area has also been reported for Cs+ exchanged HSiW
on silica and aluminosilicate supports [144]. It is noticed that, although the substitution of proton
by Cs+ increases the surface area slightly, it does not increase the acidity of the catalyst to any
extent.
54
Figure 4-6 NH3-TPD patterns for different Cs+
exchanged
Figure 4-7 Effect of different Cs+ content on
acidity of catalyst
Table 4-4 Surface area and total acidity of 10Ni/30CsxH4-xSi W/Al2O3 catalyst
Catalyst BET,
m2/g
Weak acid site
mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid
site mmol/g
/(Temp.)
Total acid
amount,
mmol/g
10Ni/30H4SiW/Al2O3 18.3 0.075/ (160oC) 0.172/ (264oC) 0.090/ (429oC) 0.337
10Ni/30Cs1H3SiW/Al2O3 22.5 0.056/ (151oC) 0.152/ (258oC) 0.108/ (400oC) 0.316
10Ni/30Cs2H2SiW/Al2O3 27.5 0.031/ (151oC) 0.075/ (213oC) 0.076/ (382oC) 0.182
10Ni/30Cs3H1SiW/Al2O3 29.1 0.027/ (152oC) - 0.050/ (442oC) 0.077
10Ni/30Cs4SiW/Al2O3 17.6 0.025/ (155oC) - 0.015/ (442oC) 0.040
Heteropoly anions (primary structure of oxoanions) can be determined by FT-IR that is an
informative fingerprint of the Keggin heteropoly cage structure to confirm the structural integrity
of the Keggin unit of these catalysts. The FTIR spectra of Keggin anions present in the catalyst
should appear between 700 and 1100cm−1 [145].
55
Figure 4-8 FT-IR spectra of (a) 30HSiW/Al2O3, (b) 10Ni/30HSiW/Al2O3, (c)
10Ni/30Cs1H3SiW/Al2O3, (d) 10Ni/30Cs2H2SiW/Al2O3, (e) 10Ni/30Cs3H1SiW/Al2O3 and (f)
10Ni/30Cs4SiW/Al2O3.
Fig. 4-8 shows the infrared spectra of the catalyst with different Cs+ content after calcination at
350oC. The fingerprint bands of the HSiW Keggin anion appeared at 978, 915, and 798 cm−1,
which could be assigned to the typical antisymmetric stretching vibrations of W=O, Si–O, and W–
Oe–W (W–Oe - stretch vibration of W-O6 octahedrons that share a vertex or an edge) [145] was
observed which provided the evidence for the retention of the Keggin ion structure on the surface
of HSiW supported catalysts. These results indicate that the Keggin structure of catalyst remains
unaltered after substitution of H+ by Cs+ on 10Ni/30HSiW/Al2O3 catalyst.
To help elucidate if the structural transformations accompany Cs+ doping, the 10Ni/30CsxH4-
xSiW/Al2O3 samples were also examined by powder XRD. The XRD pattern of Cs+ content was
depicted in the Fig. 4-9.
Fig. 4-9 provides clear evidence that recrystallization of the 10Ni/30CsxH4-xSiW/Al2O3 catalyst
accompanies Cs+ doping, consistent with proton exchange. As seen from the XRD pattern without
adding Cs+ the diffraction peaks that have been assigned to the protons of the secondary structure
were observed at 2θ=7.5o, 8.9o, 9.3o, 28.5o, 29.0o. With increasing Cs+ substitution, a variation in
the diffraction peaks was observed. It can be seen that when the amount of hydrogen protons
decreased, the intensity of the diffraction peaks assigned to the hydrogen protons decreased also.
This result is consistent with that published by Guo et. al where an increase of Cs+ content
increased the surface area of the HPAs while the acidity decreased due to substitution of protons
56
by Cs+ [146]. Meanwhile the diffraction peaks that are assigned to Cs+ substituted HSiW were
observed with 2θ diffraction bands at 10.7o, 18.5o, 23.9o, 26.2o, 30.4o, 35.8o and 39o. The intensity
of these increased with increasing Cs+ content. As a result, Cs+ containing catalysts had better
crystal stability than those without Cs+. Moreover, the greater content of Cs+ corresponded to a
more stable crystal structure [143, 147] due possibly to the modification of the crystal structure of
HSiW by the larger Cs+ radius. There is no evidence of new peaks that suggest changes in the
Keggin structure.
Figure 4-9 XRD patterns for the 10Ni/30CsxH4-xSiW/Al2O3 catalysts with different Cs+ content
Activity test results
To investigate the effect of Cs+ on the catalyst performance in the hydrogenolysis of glycerol, a
series of different Cs+ exchanged 10Ni/30CsxH4-xSiW/Al2O3 (x=0-4) catalysts were carried out in
a batch reactor for the conversion of an aqueous solution of a 30 wt% glycerol initial concentration
under an initial H2 pressure of 880 PSI. The main products observed in the liquid phase were:
acetol (Ac), 1,2-PD, 1,3-PD, 1-PO and ethylene glycol (EG). Some other products such as
methanol (MeOH), ethanol (EtOH) and minor Acrolein (Acr) were also obtained in these
experiments. Catalytic performance of the 10Ni/30CsxH4−xSiW/Al2O3 catalysts is shown in Table
4-5 and Fig. 4-10.
57
Table 4-5 Effect of Cs+ on catalytic performance in the hydrogenolysis of Glycerol
Catalyst Conv
mol%
Selectivity, mol%
1,3-PD 1,2-PD Ac EG 1-PO EtO
H
MeOH
10Ni/30HSiW/Al2O3 28.6 8.0
15.8
2.4 5.4 65.1 3.3 0.0
10Ni/30Cs1H3SiW/Al2O3 21.0 12.1 18.5 2.0 6.5 58.1 2.8 0.0
10Ni/30Cs2H2SiW/Al2O3 21.3 11.2 30.6 2.3 10.9 42.4 2.6 0.0
10Ni/30Cs3H1SiW/Al2O3 22.6 0.0 58.2 1.4 21.7 12.5 5.1 1.1
10Ni/30Cs4SiW/Al2O3 23.1 0.0 51.4 1.7 29.5 4.7 9.8 2.9
Reaction Condition: 10Ni/30CsxH4−xSiW10/Al2O3 (x=0-4) catalyst, 240ºC, 700RPM, 4g catalyst,
30g of glycerol (30wt%), 70g of DI water and 880PSI of H2, 7hours.
As seen in Table 4-5, significant difference in product distribution with respect to different Cs+
substituted catalysts was observed, although Cs+ has little effect on glycerol conversion. When
1H+ was substituted by 1Cs+, the glycerol conversion decreases from 28.6% to around 21%;
however no significant decrease in the conversion of glycerol was observed for higher
concentration of Cs+ exchanged catalysts (x=2,3,4). The pseudo first order rate constant for the
conversion of glycerol also indicates the same reactivity trend [Fig. 4-10H]. This reactivity trend
was similar to the trend in the strength of weak acid sites. However there is a clear correlation
between product distribution and the number of H+ exchanged by Cs+. The increase in the
selectivity of 1,2-PD and EG was observed for all the catalysts containing Cs+. This result suggests
that the formation of 1,2-PD and EG may be due to a competitive cleavage between the C–O
bonds and C–C bonds in the rate determining steps. Increasing the number of H+ substituted by
Cs+ increased the selectivity to EG and 1,2-PD while the selectivity to 1,3-PD and 1-PO decreased.
The selectivity to 1-PO was observed to decrease (from 65% to 4.7%) by increasing Cs+
substitution from 0 to 4, while that of the 1,2-PD and EG increased from about 20% to 52.1% and
from 6.3% to 29.9% respectively. This result indicates that selectivity to 1-PO favorably occurred
at low loading of Cs+. At high content of Cs+ the elimination of proton of the heteropolyacids
apparently suppress the further hydrogenolysis of 1,2-PD to 1-PO. Such changes in selectivity
could be attributed to the changes in the acidity of catalysts. It is clear from Table 4-4 that an
inverse correlation is observed between Cs+ content and the acidity distribution and amount over
a HSiW supported 10Ni/Al2O3 catalyst. It was also noticed that the fully substituted
58
(10Ni/30Cs4SiW/Al2O3) catalyst (i.e. 4H+ substituted by 4 Cs+) with low amount of acid sites is
essentially inactive for the production of 1-PO (selectivity to 1-PO was 4.7%). It is important to
point out that at a high level of Cs+ substitution (at 3 and 4 Cs+ substitution), no 1,3-PD was
detected. Therefore the hydrogenolysis of glycerol from 1,3-PO requires BrØnsted acid sites.
Fig. 4-10 shows the catalytic performance of the 10Ni/30CsxH4-xSiW/Al2O3 catalyst for the
hydrogenolysis of glycerol as a function of reaction time. It can be seen that as the reaction
proceeds, the conversion of glycerol and the selectivity of 1-PO gradually increase. The selectivity
of 1,2-PD (the intermediate for 1-PO) increases at the beginning of the reaction and then slightly
decreases with the reaction time. Interestingly, 1,3-PD was not detected at the first hour of
sampling but observed during the 2nd hour of sampling indicating that it is produced from an
intermediate such as 3-HPA. 1,3-PD does not convert to 1-PO readily and hence remains fairly
constant after it is produced [219]. Increasing the Cs+ content in the catalyst increases not only
the selectivity to EG but also the formation rate of this product; the more Cs+ substituted H+, the
sooner EG was formed [Fig. 4-10G]. Clearly, the selectivity to 1,2-PD and EG essentially
increased with an increase in Cs+. Hence it can be inferred that acidity plays an important role in
the hydrogenolysis of propanediols to 1-PO.
59
Figure 4-10 Effect of Cs+ on Glycerol Hydrogenolysis and products selectivity as a function of
time; A) Glycerol Conversion; B,C,D,E,F,G) Selectivity of acetol, 1,2-PD, 1,3-PD, 1-PO, other
products and EG, respectively; H) The Pseudo-First-Order rate constant k. Reaction conditions:
10Ni/30CsxH4−xSiW/Al2O3 (x=0-4) catalyst, 240ºC, 700RPM, 4g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 880PSI of H2, 7hours
One possible explanation of the Cs+ effect on EG selectivity may be due to the promotion of the
retro-aldol reaction. The formation of 1,2-PD and EG from glycerol under alkaline conditions was
reported by many authors [148-151], This reaction route involves a reversible dehydrogenation of
glycerol to glyceraldehyde (GA) on the metal surface. The product of the dehydrogenation reaction
can then undergo a C–O scission by dehydration or a C–C scission via the retro-aldol mechanism
in the aqueous phase to form 1,2-PD or EG respectively.
As shown from the experimental data, apparently the Cs-free (10Ni/30HSiW/Al2O3) catalyst
favored the C–O bond breakage leading to the formation of 1,2-PD, 1,3-PD and 1-PO instead of
EG. However, the catalysts with higher Cs+ substitution favored the cleavage of the C–C bond to
produce EG attributed to the decrease in the acidity of the catalyst. Moreover, the high EG
selectivity was obtained over high Cs+, which might originate from the decrease in acidity of the
catalyst.
60
To reveal the effect of Cs+ alone on the catalyst without the Ni hydrogenation function, a series of
different Cs+ exchanged Ni-free 30HSiW/Al2O3 (30CsxH4−xSiW/Al2O3) catalysts were prepared
and the activity of the catalysts were studied in a batch reactor for the conversion of an aqueous
solution of a 30 wt% glycerol initial concentration under an initial H2 pressure of 880 PSI.
The catalytic performance of 30CsxH4−xSiW/Al2O3 catalysts modified by different Cs+ substitution
are presented in the Table 4-6. As can be seen from Table 4-6, the support Al2O3 alone is not active
for glycerol conversion. The Ni-free (30HSiW/Al2O3) catalyst is not active for the production of
diols such as 1,2-PD, 1,3-PD or EG. Furthermore the catalyst was deactivated significantly after 2
or more H+ were substituted by Cs+. The conversion of glycerol decreased from 15.3% to only 1.1
% when all the H+ was substituted by Cs+. This was also observed by Haider et. al. for the catalytic
dehydration of glycerol to acrolein [142]. It was found that over a 0.05 M Cs+-doped HSiW
catalysts, a selectivity of acrolein of 96% at 100% glycerol conversion was obtained. However,
the catalyst was deactivated when the concentration of Cs+ increased to 0.35M and that of
selectivity to acrolein of 0% at 2% glycerol conversion was obtained. This loss of catalytic activity
may be due to hydrocarbons deposited on the active sites and/or blockage of the catalyst pores.
Without Ni for hydrogenation of the dehydrated or dehydrogenated intermediates shown in
Scheme 1 and 2, only further cracking or oligomerization to light and heavy products will occur
and cause catalyst deactivation.
Table 4-6 Effect of Cs+ on catalytic performance of 30HSiW/Al2O3 catalyst in the
Hydrogenolysis of Glycerol
Catalyst Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP
Al2O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
30HSiW/Al2O3
xCsx/Al2O3
15.3 0.0 0.0 6.0 0.0 30.5 24.8 36.7**
30Cs1H3SiW/Al2O3 13.2 0.0 0.0 6.0 0.0 35.4 26.8 31.8*
30Cs2H2 SiW/Al2O3 4.8 0.0 0.0 13.8 0.0 21.9 47.9 16.1*
30Cs3H1SiW/Al2O3 2.6 0.0 0.0 19.1 0.0 31.5 48.0 1.5*
30Cs4SiW/Al2O3 1.1 0.0 0.0 27.5 0.0 40.4 31.0 1.2*
61
Reaction Condition: 30CsxH4−xSiW10/Al2O3 (x=0-4) catalyst, 240ºC, 700RPM, 4g catalyst, 30g
of glycerol (30wt%), 70g of DI water and 880PSI of H2, 7hours. *OP: MeOH, EtOH, Unidentified
light products, **OP: MeOH, EtOH, Unidentified light and heavy products
Summary
Results of the runs with different Cs+ loading suggested that Cs+ has little effect on the glycerol
conversion; however it shows a significant effect on the product distribution – due to reduction of
acidity. The 10Ni/30HSiW/Al2O3 catalyst was found to be an effective catalyst for the production
of 1-PO, whereas, Cs+ exchanged catalyst becomes effective for the production of 1,2-PD and EG.
With an increase in Cs+ content, the selectivity for 1-PO decreases but the selectivity to 1,2-PD
and EG increases. A greater quantity of acid sites of a certain strength corresponded to a higher
selectivity of 1-PO. Although the substitution of proton by Cs+ can improve the surface area of the
catalyst to some extent, it does not enhance the catalyst activity; besides there was an inverse
correlation between Cs+ and the quantity and nature of acid sites. XRD data shows that hydrogen
protons in the secondary structure may be replaced by Cs+ that corresponds to the decrease in the
acidity of the catalyst. Although the acidity of catalyst decreases significantly, the Keggin structure
of catalyst remains unaltered after substitution of protons by Cs+ on 10Ni/30HSiW/Al2O3. Among
the catalysts tested, 1Cs+ catalyst showed the best catalytic performance for 1,3-PD and 1-PO;
however, fully substituted 10Ni/30Cs4SiW/Al2O3 is catalytically inert for production of 1-PO as it
possesses very low acid sites. Ni plays an important role for the production of lower alcohols due
to its hydrogenation activity. Without Ni, the substitution of H+ by Cs+ decreases the activity of
30HSiW/Al2O3 significantly.
4.3 Conclusions
Among the metals (Cu, Ni, Pd, and Pt) supported on 30HSiW/Al2O3, Pt is the best promoter for
the production of 1,3-PD from glycerol using. Ni a much cheaper metal has fairly comparable
reactivity to Pt. Although it is reported that Cu possesses good hydrogenation activity that is
comparable with Ni, Cu does not show activity for the production of 1,3-PD under this reaction
conditions.
62
Cs+ has little effect on the glycerol conversion; however it shows a significant effect on the product
distribution – due to reduction of acidity. The 10Ni/30HSiW/Al2O3 catalyst was found to be an
effective catalyst for the production of 1-PO, whereas, the Cs+ exchanged catalyst becomes
effective for the production of 1,2-PD and EG. A greater quantity of acid sites of a certain strength
corresponded to a higher selectivity of 1-PO. XRD data shows that hydrogen protons in the
secondary structure may be replaced by Cs+ that corresponds to a decrease in the acidity of the
catalyst. Among the catalysts tested, 1Cs+ catalyst showed the best catalytic performance for 1,3-
PD and 1-PO; however, fully substituted NiCs4SiW12O40 is catalytically inert for the production
of 1-PO as it possesses very low acid sites.
Ni plays an important role for the production of lower alcohols due to its hydrogenation activity.
Without Ni, the substitution of H+ by Cs+ decreases the activity of 30HSiW/Al2O3 significantly.
To obtain a desired product selectively, the control of reaction conditions and catalyst properties
such as acid strength, the amount of appropriate acid sites and metal hydrogenation activity will
be needed. Optimization of the catalyst preparation techniques and a balance of Ni and HiSiW
loading on various supports could lead to high yields of value-added chemicals from glycerol. 1-
PO is mainly produced from 1,2-PD with a high conversion of 1,2-PD and high selectivity to 1-
PO and 1-PO is stable under the reaction condition and is assumed as the final product in the
hydrogenolysis of glycerol using 10Ni/30HSiW/Al2O3. Due to the inexpensive Ni-based catalyst
and the high selectivity, an economical production of green and sustainable 1-PO from glycerol
hydrogenolysis may be feasible for future commercial development.
63
Chapter Five
Conversion of glycerol to lower alcohols using 10Ni/30HSiW/Al2O3
catalyst in a Hastelloy reactor
With some chemicals, notably acids, metal loss over the entire surface from the steel reactor may
occur and affect the entire experiment.The 10Ni/30HSiW/Al2O3 catalyst is a potential catalyst for
the production of higher sustainable chemicals from glycerol. However the leaching of heteropoly
species in a polar media is an issue. Due to the high acidity of the heteropoly acid, a corrosion-
resistant Hastelloy reactor was used for this study on the effect of process parameters on the
conversion and selectivity. Ni and HSiW supported alumina can serve as bifunctional catalysts
to effectively convert glycerol in a water medium under a hydrogen atmosphere. The strong acidity
of the supported HSiW facilitates the dehydration of glycerol while the moderate hydrogenation
activity of Ni allows selective hydrogenation of the aldehyde groups in the intermediate products.
In this study, we study the effect of different factors on the catalytic performance.
5.1 Repeatability of 10Ni/30HSiW/Al2O3 Catalyst
A repeatability study of the catalyst with 10Ni/30HSiW/Al2O3 has been carried out using 95%
confidence interval to ensure the experimental error is acceptable. Three experiments with this
catalyst were conducted under the same reaction conditions. The 95% confidence interval (C.I.)
and the standard deviation (σ) is calculated using Equation 5-1 and Equation 5-2 and the results
are shown in Table 5-1.
nx
nxIC
96.1,96.1..%95 Equation 5-1
n
xxi
2
Equation 5-2
64
Table 5-1 Repeatability study on 10Ni/30HSiW/Al2O3 catalyst
Run Glycerol
Conversion 1-PO Sel
1-PO
Yield
Acetol
Sel
1,2-PD
Sel.
OP
Sel
𝒙1 67.43 93.22 62.85 0.72 1.35 4.71
𝒙2 65.43 91.21 59.68 0.78 1.53 6.48
𝒙3 67.42 91.20 61.49 0.55 1.71 6.54
�̅� 66.76 91.88 61.34 0.68 1.53 5.91
σ 0.94 0.95 1.30 0.10 0.14 0.85
n
0.54 0.55 0.75 0.06 0.08 0.49
95% C.I. 66.76±1.06 91.88±1.07 61.34±1.47 0.68±0.11 1.53±0.16 5.91±0.96
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240oC, 880PSI initial H2, 30wt% (30g)
Glycerol, 2g catalyst, 7 hours.
As shown in Table 5-1, the selected catalyst exhibit perfect reproducibility in the hydrogenolysis
reaction and the 95% confidence interval for 1-PO selectivity using the 10Ni/30HSiW/Al2O3
catalyst is [90.80%; 92.95%]
5.2 Effect of experimental parameters
5.2.1 Effect of RPM
Due to the existence of a three-phase reaction, gas-liquid, liquid-solid, and intra particle diffusional
resistances may influence the rate and selectivity of the chemical reaction [152]. It is thought that
the increase in stirring rate can increases the mass transfer of gases into liquid and also from liquid
to solid surface that leads to increase in the dissolution rate of H2. Here the effect of the stirring
speed on the reaction rate of hydrogenolysis of glycerol was investigated.
Experiment condition
65
The effect of agitator speed on the overall reaction was examined by varying the agitation speed
over the range of 300 RPM to 700RPM under otherwise same reaction conditions. The experiment
was performed at 240oC under 580PSI of H2 pressure using 2g of 10Ni/30HSiW/Al2O3 catalyst,
30g of glycerol (30wt %), 70g of DI water over 7hours. Two catalysts reduced at different
temperature were studied. One was reduced at 350oC and another was reduced at 450oC for 5
hours.
Results and discussion
First the catalysts reduced at 350oC were studied. The results obtained from the hydrogenolysis of
glycerol at different agitation speed are presented in the Table 5-2 (Entry 1 to 3) and plotted in Fig.
5-1 and Fig. 5-2. The main products observed in the liquid phase were: acetol, 1,2-PD, 1,3-PD,
acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products (OP) such as methanol,
ethanol were also obtained. The data shows that using the catalyst reduced at 350oC the agitation
speed did affect the conversion of glycerol and the distribution of products. When the speed of
agitator was increased from 300RPM to 500RPM, the conversion of glycerol increased from 65%
to 84% and the selectivity to 1-PO increased from 87.2 to 91.8% respectively; where as, the
selectivity to acetol, 1,2-PD and Acr as intermediate species decreased.A further increase in stirrer
speed to 700 RPM did not affect the conversion and selectivity. This indicated that at 500RPM
external mass transfer effects were eliminated.
Table 5-2 Effect of agitator speed on the reaction rate and the distribution to products in the
hydrogenolysis of Glycerol
Red.
Temp RPM
Conv
mol%
Selectivity, mol%
13PD 12PD Acetol EG 1-PO Acr OP
350
300 64.9 0.0 1.3 0.9 0.0 87.2 5.1 5.6
500 84.3 0.0 0.0 0.5 0.0 91.8 3.8 3.9
700 81.1 0.0 0.0 0.6 0.0 90.6 3.7 5.1
450 300 41.2 0.0 3.0 1.9 0.0 80.4 9.6 5.0
700 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.5
66
Reaction Condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. OP: By-products included methanol and ethanol.
Fig. 5-1 depicts the concentration profile as a function of time of the catalyst reduced at 350oC.
From Fig. 5-1, it can be observed that as the reaction proceeds, the concentration of glycerol
decreases and the concentration of 1-PO increases. Since the concentration of acetol, 1,2-PD and
Acr was too low to be observed from Fig. 5-1, the concentration profile of acetol, 1,2-PD and Acr
are depicted separately in Fig. 5-2 to find the correlation between the intermediate species and the
speed of agitaiton.
Figure 5-1 Concentration profiles of different products using 10Ni/30HSiW/Al2O3catalyst
reduced at 350oC. Reaction conditions: 240ºC, 580 H2, 30g of glycerol (30wt %), 70g of DI
water, 2g catalyst
Figure 5-2 Concentration profiles of acetol, 12-PD and Acr using 10Ni/30HSiW/Al2O3 catalyst
reduced at 350oC. Reaction conditions: 240ºC, 580 H2, 30g of glycerol (30wt%), 70g of DI
water, 2g catalyst
67
As can be seen in Fig. 5-2, the concentration of acetol and Acr , intermediates to 1,2-PD and 1-PO
respectively, increases at the beginning of the reaction and then decreases with the reaction time
and did not depend on the agitation speed. However, the pattern of 1,2-PD concentration is not
similar to acetol concentration. When the agitation speed is low at 300RPM, 1,2PD is still
detectable and the concentration of 1,2-PD as the intermediate of 1-PO increases at the beginning
of the reaction and then decreases with the reaction time. However, when the speed was increased
to 500RPM, 1,2-PD became undetectable. Furthermore an increase in the agitation speed to 700
RPM did not result in an increase in the conversion of glycerol; however it still affected the product
distribution slightly and 1,2-PD was also undetectable. The selectivity to 1-PO slightly decreases
while the selectivity to by products increases. This decrease in the 1-PO selectivity could be due
to the formation of by-products such as methanol and ethanol through side reactions.
Results showed that a speed of 500RPM is sufficient to allow further hydrogenolyis of 1,2-PD or
hydrogenation of Acr to 1-PO but not increase the side reactions to produce by products. There
are always other by-products formed during the reaction time. The pseudo-first-order rate constant
also provides evidence of the effect of stirring speed on the reaction rate (Fig. 5-3).
Catalysts reduced at 450oC were also studied to see if the stirring speed still affects the
hydrogenolysis of glycerol. The data is presented in the Table 5-2 (entry 4and 5). It is evident that
increasing the reduction temperature decreases the catalyst activity significantly; however the
performance of the catalyst was independent of agitation speed over the range of 300 RPM to 700
RPM, and the reaction rate is almost identical (Fig. 5-3). It is noted that the agitation speed did not
result in a change in both the conversion of glycerol and the distribution of products; the conversion
of both catalysts is around 42%.
Normally, if a process is controlled by diffusion, the reaction rate would also linearly increase with
increasing stirring speed; whereas if the process was controlled by chemical reaction, reaction rate
will no longer change when the stirring speed reaches a certain value [153]. In the case of when
the catalyst is reduced at 350oC, as can be observed from the data when the stirring speed was
lower than 500 RPM, the reaction rate constant k increases with stirring speed increasing, the
glycerol concentration decreased faster at 500-700 RPM compared with 300 RPM (Fig. 5-3).
When the stirring speed was over 500 rpm, the reaction rate constant k seems to be constant and
does not change much with stirring speed.
68
By increasing stirring rate, the mass transfer of reactants (glycerol, H2) from the bulk to catalyst
surface is increased. The H2 was supplied continuously throughout the entire experiment so the
quantity of H2 was sufficient for the entire experiment. Therefore most probably the rate of reaction
at stirring rates higher than 500 RPM is controlled by a surface reaction and mass transfer should
not be an issue. However, a similar phenomenon was not observed on the catalyst reduced at 450oC
and it is suggested that the rate of reaction of this catalyst is controlled by the surface reaction even
at 300 RPM since the conversion is slower for this catalyst.
Figure 5-3 Pseudo-First-Order kinetic analyses in the presence 10Ni/30HSiW/Al2O3 catalysts at
different agigator spead. Reaction condition: 240ºC, 580 H2, 30g of glycerol (30wt%), 70g of DI
water, 2g catalyst
69
Summary
This study showed that at stirring speeds higher than 500RPM the diffusion process was much
faster than the chemical reaction, and diffusion was not the limiting factor for the reaction. Hence
a stirring speed of 500RPM is sufficient to overcome diffusional limitations for the hydrogenolyis
of glycerol to the products for the catalyst reduced at 350oC. However, for the catalyst reduced at
450oC even at 300 RPM the hydrogenolysis catalyzed by this catalyst is already chemically
controlled.
5.2.2 Effect of hydrogen pressure
Molecular hydrogen is a reactant in hydrogenolysis reactions. High hydrogen pressure will
increase the cost of purchase, transportation and storage of gaseous hydrogen. Optimizing
hydrogen can bring about a number of different benefits and add value to the process. Therefore,
a minimum hydrogen pressure in the reactor is required for complete catalytic conversion of
glycerol to desired products. Above this hydrogen pressure, catalytic reaction rates are expected
to be independent of hydrogen pressure due to the limited adsorption capacity of the catalyst.
Therefore optimal operating pressures for hydrogenolyis of glycerol to other products will balance
the higher costs of high pressure equipment with decreased yields at lower pressures. Here the
effect of H2 pressure on reaction rate of hydrogenolysis of glycerol was investigated for different
pressures of hydrogen over the range 290 - 800 PSI.
Experimental condition
The effect of hydrogen pressure pressure on the overall reaction is studied by carrying out the
hydrogenlolysis of glycerol at 290, 580 and 800PSI of hydrogen pressure under otherwise the same
reaction conditions. The experiment was performed at 240oC under the selected H2 pressure using
2g of 10Ni/30HSiW/Al2O3 catalyst, 30g of glycerol (30wt%), 70g of DI water, over 7hours. Prior
to the experiment the catalyst was reduced at 350oC for 5 hours.
Results and discussion
70
The effect of hydrogen pressure on the catalytic performance of 10Ni/30HSiW/Al2O3 catalyst is
listed in the Table 5-3 and Fig. 5-4. The main products observed in the liquid phase were: acetol,
1,2-PD, 1,3-PD, acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products (OP) such
as methanol (MeOH), ethanol (EtOH) were also obtained. However at low H2 pressures of 290PSI,
some other light unidentified products (UIP) were also detected.
Table 5-3 Effect of hydrogen pressure on the conversion of glycerol and the distribution to
products in the hydrogenolysis of glycerol
PH2
PSI
kobs o
s-1 Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP
0 22.9 0.0 0.0 17.3 0.0 13.9 13.4 55.4*
290 8.94E-5 87.5 0.0 1.5 1.8 0.0 76.9 8.1 11.7*
580 7.00E-5 81.1 0.0 0.0 0.6 0.0 90.6 3.7 5.1**
800 3.41E-5 53.7 0.9 1.2 0.6 0.0 92.9 1.6 2.8**
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water, and H2, *OP: MeOH, EtOH and light unidentified, **: EtOH, MeOH
As can be seen from the Table 5-3, the hydrogen pressure dramatically influenced both the glycerol
conversion and the distribution of products; the conversion of glycerol and selecitivty to
intermediae species such as acetol, 1,2-PD and Acr decreased monotonously with increasing
hydrogen pressure; whereas, the selectivity to 1-PO increased. Without H2 (under N2), the
conversion of glycerol and selectivity to 1-PO is low (22.9% and 13.9% respectively), selectivity
to acetol and acrolein is high (17.3% and 13.4% respectively) and significant by-products were
produced. Once H2 (290PSI) was introduced, the conversion of glycerol and selectivity to 1-PO
siginificantly increased to 87.5% and 76.9% respectively. It’s thought that H2 promotes the
hydrogention of intermediate species so drives the hydrogenolysis reaction forward led to an
increase in the conversion of glycerol. However, a further increase of H2 pressure caused a
decrease in the conversion of glycerol. At low H2 pressure of 290PSI, although the conversion of
glycerol is high of 87.5% but the selectivity to 1-PO is much lower (76.9%); the selectivity of
71
acetol and Acr is also high compared to other H2 pressures. When the H2 pressure was increased
from 290PSI to 580PSI the selectivity to 1-PO significantly increased from 76.9% to 91.7%, but
the conversion of glycerol decreased from 87.5% to 72.3% respectively. A further increase of H2
pressure to 800PSI caused a decrease in the conversion of glycerol to only 53.7%; however, it only
affects slightly the selectivity to 1-PO, the selectivity to 1-PO increases about 1% from 91.7% to
92.6%; 1,3-PD starts to be produced; meanwhile the selectivity of Acr decreased significantly to
1.6%. The abundance of Acr (8.1%) at a low H2 pressure of 290PSI and this Acr significantly
decreased to 1.6% at a high H2 pressure of 800PSI suggesting that at low H2 pressure,
hydrogenation has a low rate compared to the one was at high pressure (Since hydrogen was
supplied continuously throughout the reation, the quantity of H2 was sufficient for the entire
experiment). It’s again believed that 1-PO was produced by hydrogenation of Acr. The glycerol
conversion and product selectivity as a function of time are shown in Fig. 5-4.
It can be observed from Fig. 5-4 that when the H2 pressure is increased from 290PSI to 800PSI,
the selectivity to 1-PO (E) is increased but the selectivity to acrolein (F) is decreased. This maybe
due to the fact that H2 promotes the hydrogenation of acrolein to 1-PO. This result was consistent
with that of Mengpan et al [154] reported in their paper which reported on a study of the catalytic
transformation of glycerol to 1-PO over the two layer catalysts (ZrP, coupling with 2%Ru/SiO2).
The selectivity of 1-PO was enhanced from 32.0% to 76.5% while the selectivity of Acr decreased
sharply from 47.2% to 2.3% as the hydrogen pressure was increased from 0.5 MPa to 2 MPa, the
hydrogenation rate of the second layer of the 2%Ru/SiO2 catalyst increased greatly. They found
that the Acr conversion was more than 99% and the selectivity to 1-PO reached 96% using Ru/SiO2
catalyst with the feed of 10% acrolein in a fixed-bed reactor, at temperature 315oC; H2 pressure of
2 MPa and suggested that the hydrogenation of Acr to 1-PO is a fast reaction.
72
73
Figure 5-4 Effect of H2 pressure on glycerol hydrogenolysis and products selectivity as a function
of time: a) Glycerol conversion; B,C,D,E,F,G) Acetol, 1,2PD, 1,3-PD, 1-PO, Acr and OP
selectivity respectively; Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g
catalyst, 30g of glycerol (30wt%), 70g of DI water and H2.
It is reported that the solubility of hydrogen in water is proportional to the hydrogen pressure [155];
so it is expected that a high conversion of glycerol should be observed at high H2 pressure.
However in this work the reaction rate (Fig. 5-5) decreased with an increase in H2 pressure. It is
suggested that an increase in H2 pressure may promote the reduction of W resulting in lower acidic
activity towards the dehydration step that decreases the conversion of glycerol [209]. Silicotungstic
acid single crystals can be reversibly reduced to heteropolyblues as reported by Karwowska et al.
[156]. Indeed, it was observed that at high pressure of H2, the solution of the product and the
catalyst itself became a darker blue colour than it was at low pressure indicating a higher
concentration of heteropolyblues. Although there is a decrease in glycerol conversion at high
pressure, it is believed that the high H2 pressure is necessary for hydrogenation step, to suppress
side reactions and decrease the formation of undesired products. Therefore an optimal operating
H2 pressures is required to obtained high yield of 1-PO. It was found that reductive conditions
(under hydrogen) are rather unfavorable [157] for the thermal stability of the HPA at higher
temperatures.
74
Figure 5-5 Pseudo-First-Order kinetic plots of H2 pressure effect on hydrogenolysis of glycerol in
the presence of 10Ni/30HSiW/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM, 2g catalyst,
30g of glycerol (30wt%), 70g of DI water and H2
Summary
It can be seen that the conversion of glycerol is inversely proportional to the hydrogen pressure at
pressure higher than 290PSI. This can possibly be attributed to increased hydrogen pressures
75
actually inhibited the reactions due to competitive adsorption of hydrogen to the catalyst surface
and the displacement of intermediate products , or the reduction of W under high pressure of H2
results in the reduction of activity of the catalyst for the dehydration step. However a high H2
pressure is necessary to suppress the undesired dehydration or side reactions and decrease the
undesired products. Optimal operating H2 pressures are required to obtained high yield of 1-PO.
5.2.3 Effect of water content
Water is not only a solvent for the reaction but also a product of the hydrogenolysis of glycerol.
Removal of water from the product drives the hydrogenolysis reaction forward. Besides it is
preferable to use a concentrated feed in order to reduce the energy cost of heating water and to
increase reactor efficiency (reactor space time). Therefore in this part the effect of water content
(aqueous glycerol feed concentration) on the overall reaction was selected for study on the impact
of diluents.
Experimental condition
The effect of water content on the overall reaction is studied by carrying out the hydrogenlolysis
of glycerol at 20, 40, 70, 90wt % water under the otherwise the same reaction conditions. The
experiment was performed at 240oC under 580PSI H2 pressure using 2g (6.5wt%) of
10Ni/30HSiW/Al2O3 catalyst, 30g of glycerol, for 7hours. The catalysts were reduced at 450oC for
5h.
Results and discussion
Table 5-4 provides a summary of the effect of initial water content on overall glycerol conversion
and product distribution. The main products observed in the liquid phase were: acetol, 1,2-PD, 1,3-
PD, acrolein (Acr) and 1-PO. Some other products (OP) such as methanol (MeOH), ethanol
(EtOH) and ethylene glycol (EG) were also obtained.
As can be seen from the Table 5-4, Fig 5-6 and Fig 5-7, as the water content increased, the
conversion of glycerol and selectivity to both 1,2-PD and acrolein decreased. This may be due to
the fact that as water content is increased, the equilibrium is driven in the backward direction.
However, the selectivity to 1-PO slightly increased.
76
Table 5-4 Effect of water content on the conversion of glycerol and the distribution to products in
the hydrogenolysis of Glycerol
Water
wt%
kobs
s-1
Conv
mol%
Selectivity, mol%
13PD 12PD Acetol 1-PO Acr. OP*
20 3.25E-5 54.0 0.0 3.9 1.2 72.1 5.9 16.9
40 2.78E-5 48.3 0.0 3.4 1.2 76.5 5.4 13.5
70 2.46E-5 43.8 0.0 2.9 1.2 80.9 5.4 9.6
90 1.92E-5 36.4 0.0 5.9 0.0 81.2 2.2 10.7
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 30g of glycerol, 6.5wt%
catalyst (2g), 7 hours, and 580PSI of H2. *OP: By-products included methanol, ethanol and EG
Figure 5-6 Effect of water content on Glycerol Hydrogenolysis and product distribution; Reaction
condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 30g of glycerol, 6.5wt% (2g) of
catalyst and 580PSI H2.
Dilute feed solutions increase the selectivity to 1-PO but decrease the conversions of glycerol and
intermediate species of acrolein and 1,2-PD or vice versa. This changing tendency can be
explained: the decrease of water content leads to an increase in the glycerol conversion so the yield
of 1,2-PD and/or acrolein as a primary product will increase. However 1,2-PD and/or acrolein is
suggested as an intermediate species to 1-PO, so the amount of 1,2-PD and/or acrolein increases
with increasing glycerol concentration, while the available number of catalytic sites (i.e., the
77
amount of catalyst) is constant. As a result, less active sites becomes available for the conversion
of 1,2-PD and/or acrolein to 1-PO, so more 1,2-PD and/or acrolein can be retained and less 1-PO
is produced. Based on stoichiometric calculation (Scheme 5-1), it is showed that 1 mol of H2 is
required to convert 1 mol of 1,2-PD to 1mol of 1-PO but it is required 2 mol of H2 to convert 1
mol of Acr to 1mol of 1-PO. Although it is required more H2 to convert an intermediate specie of
acrolein to 1-PO than to convert of 1,2-PD to 1-PO, for the entire reaction it will need the same
amount of H2 whether 1-PO is obtained from 1,2-PO or acrolein, i.e. 2 mol of H2 is required to
produce 1 mol of 1-PO from 1 mol of glycerol.
Scheme 5-1 The production of 1-PO from 1,2-PD and Acr
78
Figure 5-7 Pseudo-First-Order kinetic plots of the effect of water content feed concentration on
hydrogenolysis of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst; Reaction condition:
240ºC, 700RPM, 30g of glycerol, 2g (6.5wt%) of catalyst, and 580PSI H2
Summary
Dilute feed solutions increase the selectivity to 1-PO but lower the conversions of glycerol.
Increasing the glycerol concentration (decreasing the initial water content) decreased the
selectivity to 1-PO but the selectivity to 1,2-PD and acrolein increased. The increase in the
concentration of glycerol results in less active sites becoming available for the conversion of 1,2-
79
PD and/or acrolein to 1-PO. Optimal glycerol feed concentration is required to obtained a high
yield of 1-PO.
5.2.4 Effect of catalyst weight loading
The amount of catalyst present in the reaction mixture is an important parameter that influences
the rate of reaction. The amount of solid catalyst determines the total amount of surface area of the
catalyst and the number of sites available for the reaction. When the amount of catalyst increases
the amount of sites available for the reactants to get adsorbed onto and react also increases. In this
part of the research, reactions were performed to determine the impact of catalyst loading on
conversion of glycerol to other products.
Experiment condition
The effect of catalyst loading on the overall reaction is studied by carrying out the hydrogenlolysis
of glycerol using a different weight of catalyst over the range of 2.5, 4.5 and 6.5 wt% under
otherwise the same reaction conditions. The experiment was performed at 240oC, 700 RPM under
580 H2 pressure using 10Ni/30HSiW/Al2O3 catalyst, 30g of glycerol (30wt. %), 70g of DI water,
for 7hours.
Results and discussion
Table 5-5 and Fig. 5-8 provide a summary of the effect of catalyst loading on the overall glycerol
conversion and product distribution. The main products observed in the liquid phase were: acetol,
1,2-PD, 1,3-PD, Acr, 1-PO and EG. Some other products (OP) such as methanol (MeOH), ethanol
(EtOH) were also obtained.
Table 5-5 Effect of catalyst loading on the conversion of glycerol and the distribution to products
in the hydrogenolysis of glycerol
Cat
wt%
Conv
mol%
kobs, s-1
E-5
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP*
2.5 55.4 3.62 0.0 0.0 1.0 0.0 90.6 5.1 3.2
4.5 68.7 5.13 0.0 0.8 0.7 0.0 92.0 3.5 3.1
80
6.5 81.1 7.00 0.0 0.0 0.6 0.0 90.6 3.7 5.1
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 30g of glycerol, 70g of DI
water and 580PSI of H2. *OP: By-products included methanol and ethanol
Figure 5-8 Effect of catalyst weight loading on Glycerol Hydrogenolysis and product distribution;
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 30g of glycerol (30wt%),
70g of DI water and 580PSI H2.
Figure 5-9 Pseudo-first-order kinetic plots of effect of catalyst weight loading on hydrogenolysis
of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM,
30g of glycerol (30wt%), 70g of DI water, and 580PSI H2
81
As can be seen, while the glycerol conversion increased monotonously with increasing catalyst
loading, the product distribution is only affected slightly. The selectivity to acetol decreased with
an increase in catalyst loading, and the selectivity to by products is the lowest at 4.5% catalyst
loading. It is suggested that higher catalyst loading provides more active sites for the
hydrogenolysis reaction of both glycerol to 1,2-PD and 1,2-PD can undergo further hydrogenolysis
to propanol. However, further increases in catalyst loading could provide excess active sites
resulting in increased exposure of 1-PO to produce undesired products causing a slight increase in
selectivity of by-products. According to Fig. 5-9, it is also evident that the reaction rate of the
hydrogenolysis reaction increased with an increase in catalyst loading.
Summary
Conversion increased with catalyst loading, but selectivity had a maximum of 92.7% at 4.5%
loading. It is assumed that high catalyst loadings may result in an increase in the decomposition of
the desired product or promote side reactions. Optimal catalyst loading is required to obtain a high
yield of 1-PO.
5.2.5 Kinetic analysis
Based on the sampling data, the rate constant and the kinetics could be determined.
For the reaction of glycerol and H2 the reaction to produce 1-Propanol can be written as:
Glycerol + 2H2 → 1-PO + 2H2O
The empirical rate law will be of the form:
−𝑑[𝐺𝐿]
𝑑𝑡 = k[GL]a[H2]
b[H2O]c[cat]d
where a, b, c, d are the reaction orders with respect to Glycerol, H2, H2O and catalyst respectively
Since [cat], [H2] and [H2O] are constant,
−𝑑[𝐺𝐿]
𝑑𝑡 = kobs[GL]a
where kobs = k[H2]b[H2O]c[cat]d
82
we will have a new constant that is called kobs since this will be the rate constant that we “observe”
in our experiment.
The effect of catalyst weight loading was studied. As can be seen from Fig. 5.9A the experimental
data showed ln[GL] vs. time is a straight line, thus it is suggested that the reaction is first-order in
GL. The plot of ln[GL] vs. time is represented by the equation 5-1.
−𝑑[𝐺𝐿]
𝑑𝑡 = kobs[GL] (5-1)
To study the reaction order with respect to catalyst, 1/[H2], and 1/[H2O], a set of observed rate
constants of catalyst, 1/[H2], and 1/[H2O] are presented in Table 5-5, 5-3 and 5-4. The values of
the observed rate constants were plotted as a function of each parameter respectively (Figure 5-
9B, 5-5C and 5-7C). If the order of the reaction with respect to catalyst, 1/[H2], and 1/[H2O] is 1
then it is expected that kobs vs each parameter will be a linear, otherwise the order of reaction is
not 1. The data that are shown in each figure (Fig. 5-9B, 5-5C and 5-7C) indicate that the reaction
is first order with respect to catalyst, 1/[H2], and 1/[H2O]; and we can obtain the actual rate constant
from the slope of the line.
Therefore, the rate of glycerol disappearance is:
−𝑑[𝐺𝐿]
𝑑𝑡 = k
[𝐺𝐿][𝑐𝑎𝑡]
[𝐻2][𝐻2𝑂]
PH2 and [H2O] are constant, and then
−𝑑[𝐺𝐿]
𝑑𝑡 = kobs[GL] where kobs= k
[𝑐𝑎𝑡]
[𝐻2][𝐻2𝑂]= kcat[cat], where kcat= k
1
[𝐻2][𝐻2𝑂] (5-2)
From Fig. 5-9B on plotting the value of the observed rate constants as a function of catalyst
loading, we found that the actual rate constant from the slope of the line is kcat=2.7E-5 s-1g-1. Then
−𝑑[𝐺𝐿]
𝑑𝑡 = 2.7E-5[cat][GL]
From (5-2) we have
k=kcat[H2][H2O]=2.7E-5s-1g-1.4MPA.41.5mol.l-1 = 4.5E-3s-1g-1MPa.mol.l-1
Catalyst loading and [H2O] are constant, and then
83
−𝑑[𝐺𝐿]
𝑑𝑡 = kobs[GL] where kobs= k
[𝑐𝑎𝑡]
[𝐻2][𝐻2𝑂]= kH2
1
[𝐻2], where kH2= k
[𝑐𝑎𝑡]
[𝐻2𝑂] (5-3)
From Fig. 5-5C on plotting the value of the observed rate constants as a function of H2, we found
the actual rate constant from the slope of the line is kH2=2.1E-4 MPa.s-1.
From (5-3) we have
k=kH2
[𝑯𝟐𝑶]
[𝒄𝒂𝒕] = 2.1E-4MPa.s-1.41.5mol.l-1.(1/2)g-1= 4.3E-3g-1s-1MPa.mol.l-1
Catalyst and [H2] are assumed constant, and then
−𝑑[𝐺𝐿]
𝑑𝑡 = kobs[GL] where kobs= k
[𝑐𝑎𝑡]
[𝐻2][𝐻2𝑂]= kH2O
1
[𝐻2𝑂], where kH2O= k
[𝑐𝑎𝑡]
[𝐻2] (5-4)
From Fig. 5-7C, on plotting the value of the observed rate constants as a function of H2O, we found
that the actual rate constant from the slope of the line is kH2O=2.0E-4 mol.l-1.s-1.
From (5-4) we have k=kH2O
[𝑯𝟐]
[𝒄𝒂𝒕] =2.0E-4 mol.l-1.s-1.4MPa.(1/2)g-1=4.0E-4g-1s-1MPa.mol.l-1
The results showed that the actual rate constant are similar when (H2O, H2) or (catalyst, H2O) are
kept constant and k ~ 4.5E-3 s-1g-1MPa.mol.l-1. However, when the catalyst and H2 were
constant, the actual rate constant becomes lower and k~ 4.0E-4 s-1g-1MPa.mol.l-1. The reason
may be because for this set of experiments the catalysts were reduced at high temperature of
450oC, while for other two sets of experiments (when catalyst and [H2O] or [H2O] and [H2] were
kept constant) the catalysts were reduced at lower temperature of 350oC. It is observed from the
section 6.2.2 that the catalyst loses its acidity that results in the loss of its activity when it is
reduced at temperature above 400oC. Therefore the actual rate constant of the reaction using the
catalyst reduced at 450oC is lower than that of the reaction using the catalyst reduced at 350oC.
5.2.6 Effect of temperature and activation energy
Temperature plays an important role in the hydrogenolysis of glycerol. Since temperature can
affect the rate of the hydrogenation. Increasing temperature leads to change in rates of adsorption,
desorption that can cause a change in hydrogenation step and the overall reaction. In this section,
the reactions were performed to determine the impact of temperature on the rate of the
84
hydrogenolysis of glycerol to other products. The value of the activation energy was also
calculated.
Experimental condition
The effect of temperature on the overall reaction is studied by carrying out the hydrogenlolysis of
glycerol at 230 to 260oC under the otherwise the same reaction conditions. The experiment was
performed at 580PSI H2 pressure using 2g of 10Ni/30HSiW/Al2O3 catalyst, 30g of glycerol
(30wt%), 70g of DI water, for 7hours. The catalysts were reduced at 400oC for 5 hours.
Results and discussion
The effect of temperature on the catalytic performance of the 10Ni/30HSiW/Al2O3 catalyst is
presented in the Table 5-6 and Fig. 5-10. The main products observed in the liquid phase were:
acetol, 1,2-PD, 1,3-PD, Acr, 1-PO and EG. Some other products (OP) such as methanol (MeOH),
ethanol (EtOH) were also obtained.
As can be seen, the temperature affects significantly the conversion of glycerol and the degradation
of 1,2-PD. The glycerol conversion and by-products increased monotonously with increasing
catalyst loading, while the selectivity to 1,2-PD and acetol decreased. At 260oC, the conversion of
glycerol reached 100%. On.increasing temperature from 230oC to 260oC the selectivity of 1,2-PD
decreased from 2.9% to an undetectable level, meanwhile the selectivity to 1-PO slightly increased
initially and then went through a maximum of 91.2% at 240oC. Further increases in temperature
from 250oC to 260oC decreased the selectivity of 1-PO significantly to 84.2% at 100% conversion
of glycerol.
Although high temperature favors 1-PO production, it also promotes the degradation of 1-PO.
Over the range of 230 to 250oC, the effect of temperature on the selectivity to 1-PO distribution
was not significant (selectivity to 1-PO reaches around 90%). However at higher temperature of
260oC the degradation of 1-PO occurs significantly, more than other light products which were
produced leading to a decrease in selectivity of 1-PO to 84.2% and an increase in selectivity to
other products (9.1%). This indicated that at a high temperature of 260oC, excessive
hydrogenolysis resulted in the degradation of 1-PO or in increase side reactions.
85
Table 5-6 Effect of temperature on the conversion of glycerol and the distribution to products in
the hydrogenolysis of glycerol
T,oC Conv.
mol%
Selectivity, mol%
13-PD 12-PD Acetol EG 1-PO Acr OP*
230 53.0 0.0 2.9 0.9 0.0 90.3 2.2 3.7
240 67.4 0.0 1.7 0.6 0.0 92.4 1.6 3.7
250 91.2 0.0 0.0 0.4 0.0 90.8 2.8 6.0
260 100.0 0.0 0.0 0.4 1.2 84.8 4.5 9.1
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water, 580PSI of H2, 7hours. *OP: By-products included methanol and
ethanol.
86
Figure 5-10 Effect of temperature on glycerol hydrogenolysis and products selectivity as a
function of time; A) Glycerol Conversion; B,C,D,E,F) Selectivity of acetol, 1,2-PD, Acr., 1-PO,
other products, respectively; Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM,
2g catalyst, 30g of glycerol (30wt%), 70g of DI water and 580 PSI of H2.
Activation energy
Based on the analyses of Pseudo-First-Order kinetic, the observed rate constants at different
reaction temperature, and the activation energy for the 10Ni/30HSiW/Al2O3 catalyst was
calculated and is presented in Table 5-7.
Table 5-7 Effect of temperature on the reaction rate of hydrogenolysis of glycerol
T,oC kobs, s-1 T (K) 1/T*K-1 Ln(kobs)
230 3.30 E-05 503 0.00199 -10.32
240 4.77 E-05 513 0.00195 -9.95
250 1.14 E-04 523 0.00191 -9.08
260 1.58 E-04 533 0.00188 -8.75
Ea/R is the slope of the line given in the Fig 5-12. The activation energy is Ea = 124.1 kJ/mol. Up
to date there is no work has done on the activation energy for the hydrogenolysis of glycerol to 1-
PO.
Summary
It was shown in this study that with an increase in temperature from 230 to 260oC, there was a
remarkble increase in the glycerol conversion from 53 to 100%. The selectivity of 1,2-PD
87
decreased gradually with an increase in temperature and was undetectable at 250oC. This indicated
that 1,2-PD mostly undergoes hydrogenolysis to form 1-PO at 250oC. The selectivity of 1-PO was
stable at around 90% until 250oC but significantly drop from 90% to 84% at 260oC. This suggests
that 1-PO may be degraded at high temperature of 260oC.
Increasing temperature may promote further hydrogenolsis of 1,2-PD to 1-PO. However excessive
heat may cause the degradation of 1-PO to other products or other side reaction. Therefore it is
suggested that operation at higher pressures may prevent degradation of products. It is found that
the activation energy of the hydrogenolysis of glycerol to 1-PO using a catalyst of
10Ni/30HSiW/Al2O3 is of 124.1 kJ/mol and it is chemically kinetically controlled.
Figure 5-11 Pseudo-first-order kinetic analysis for the 10Ni/30HSiW/Al2O3 catalysts at different
temperature (230, 240, 250 and 260oC). Reaction condition: 240ºC, 580PSI of H2, 700RPM, 2g
of catalyst, 30g of glycerol (30wt%), 70g of DI water.
Figure 5-12 Calculation of the activation energy based on ln(kobs) and 1/T using the equation
lnk=lnA-Ea/R(1/T)
88
5.3 Study of the effect of NiHSiW/Al2O3 loading on Al2O3
Bifunctional catalysis involving successive chemical steps on two independent types of sites plays
an important role for hydrogenolysis of glycerol. The investigation of the effect of metal–acid
balance on bifunctional catalysts is important.
Therefore, the effect of active component content was studied by varying the weight loading of
HSiW and Ni to find out the effect of component content and the optimum composition. First the
weight loading of HSiW was studied and then the optimum HSiW weight loading was chosen to
study the effect of Ni loading. The active components were added in sequence so the effect of the
sequence of adding the active component was also studied.
5.3.1 Effect of HSiW loading on catalytic activity of the 10Ni/HSiW/Al2O3
In this part the effect of HSiW loading on the catalyst activity of 10Ni/HSiW/Al2O3 for the
hydrogenolysis of glycerol was studied. The weight loading of HSiW on the catalysts was varied
from 0 to 30wt% while the loading of Ni is set at 10wt% in order to investigate the influence of
HSiW loading on the catalytic activities of the 10Ni/HSiW/Al2O3 catalysts.
Experimental condition
The effect of HSiW loading on the catalyst activity was studied by varying the weight loading of
HSiW on the catalysts from 0 to 30wt%, the hydrogenolysis of glycerol was carried out at 290,
580 and 800PSI of hydrogen pressure under otherwise the same reaction conditions. The
experiment was performed at 240oC under 580PSI H2 pressure using 2g of 10Ni/30HSiW/Al2O3
catalyst, 30g of glycerol (30wt%), 70g of DI water, for 7hours. The catalysts were reduced at
450oC for 5 hours.
Results and discussion
The conversion of the glycerol and product distribution observed as a function of time at different
HSiW loadings are shown in Fig. 5-13 and the data are summarized in Table 5-8. The main
products observed in the liquid phase were: acetol, 1,2-PD, 1,3-PD, Acr, 1-PO and EG. Some other
products (OP) such as methanol (MeOH), ethanol (EtOH) were also obtained.
89
The Fig 5-13 shows that for all catalysts, as the reaction proceeds, the conversion of glycerol and
the selectivity of 1-PO gradually increase (Fig 5-13 A and D), while the selectivity of acetol, 1,2-
PD and acrolein (the intermediate species) increases at the beginning of the reaction and then
slightly decreases with increasing reaction time (Fig 5-13 B, C and E).
Table 5-8 Effect of HSiW loading on the conversion of glycerol and the distribution to products
in the hydrogenolysis of glycerol using 10Ni/Al2O3
Reaction condition: 10Ni/xHSiW/Al2O3 catalyst (x=0, 2.5, 5, 10, 20 and 30wt%), 240ºC,
700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and 580PSI of H2.* OP: By-
products included only MeOH and EtOH
As can be seen from the Table 5-8, the variation of HSiW loading over the range from 0 to 30wt%
influences both the glycerol conversion and the product distribution. The selectivity to acetol, Acr
and 1-PO gradually increased with an increase in HSiW loading. However the conversion of
glycerol and selectivity of by-products first increased and then decreased, both of them went
through a maximum of 58.2% and 58.5% respectively at 2.5wt% of HSiW loading. The selectivity
to 1,2-PD and EG also went through a maximum of 25.2% and 23% respectively at 5wt% HSiW
loading. Using the HSiW-free catalyst (i.e. Ni/Al2O3) and low loading of HSiW of 2.5wt%, the
primary product was by products (mainly ethanol) with a selectivity of 51.1%, whereas only minor
amount of 1-PO (13%) was obtained. This result suggested that at low HSiW loading (below
10wt%) the sequential hydrogenolysis capability of HSiW supported Ni/Al2O3 catalyst was not
effective to catalyze the sequential hydrogenolysis of 1,2-PD to 1-PO. Besides, the catalyst was
also not active for the production of acrolein through the consequence dehydration of glycerol and
HSiW,
wt%
Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP*
0 51.6 0.0 23.8 0.6 11.5 13.0 0.0 51.1
2.5 58.2 0.0 9.7 0.5 12.3 18.7 0.3 58.5
5 39.5 0.0 25.2 0.8 23.0 23.2 0.6 27.2
10 37.2 0.0 17.5 1.0 17.0 37.1 1.0 26.4
20 39.8 0.0 5.4 1.1 5.3 69.2 3.4 15.6
30 43.8 0.0 2.9 1.2 0.0 79.7 5.4 10.8
90
the selectivity to acrolein is low, being less than 1%. This maybe due to the low acidity of the
catalyst at low HSiW loading.
91
Figure 5-13 Effect of HSiW loading on Glycerol Hydrogenolysis and products selectivity as a
function of time; A) Glycerol Conversion; B,C,D,E,F,G) Selectivity of acetol, 1,2-PD, 1-PO, Acr.,
other products, respectively. H) A comparison in catalytic performance. Reaction condition:
10Ni/HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI
water and H2.
Figure 5-14 Pseudo-First-Order kinetic plots of effect of HSiW loading on hydrogenolysis of
glycerol in the presence of 10Ni/HSiW/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM, 30g
of glycerol (30wt%), 70g of DI water, 2g catalyst, and 580PSI H2
With a loading of HSiW higher than 10wt% the sequential hydrogenolysis capability of the catalyst
was elevated considerably and the sequence of dehydration of glycerol was also promoted. As can
be seen, when the loading of HSiW was below 10wt% the selectivity to 1-PO and Acr is as low as
37.1% and 1% respectively at 37.2% conversion of glycerol. When the HSiW loading was
92
increased to 20wt% the glycerol conversion increased slightly to 39.5% but 1-PO and Acr
selectivity jumped up to 70.2% and 3.4% respectively. The selectivity to 1-PO and Acr reached
the highest value of 80.9% and 5.4% at 43.8% conversion of glycerol with 30wt% HSiW loading.
It is suggested that the loading of HSiW should be higher than 20wt% to promote the further
hydrogenlolysis of 1,2-PD to 1-PO or the production of Acr for the sequence of dehydration of
Acr to 1-PO. It is believed that such changes in selectivity are likely related to the acidity of
catalysts. Hence it is believed that HSiW played an important role in the production of 1-PO.
Characterization of catalysts
Acid properties of the catalyst with different HSiW content were explored by NH3-TPD from 50
to 750◦C to determine the quantity of acid sites on the catalyst surface and the distribution of acid
strengths of the catalyst and thus, to find a comprehensive correlation between HSiW content with
catalytic activity and acid property of the 10Ni/xHSiW/Al2O3 catalysts. Fig. 5-15 shows the
profiles of NH3 desorbed from the studied catalysts. The correlation between the loading of HSiW
and acidity of the catalyst are depicted in the Fig. 5-16A. The TPD data was deconvoluted into 3
peaks (namely weak, medium and strong acid sites) using a Gaussian fitting method, the quantity
of acid sites of the catalysts is recorded in Table 5-9 and was then correlated with the catalytic
activity of the catalysts.
Figure 5-15 NH3-TPD patterns of different HSiW loading
93
Figure 5-16 A. Effect of HSiW loading on acidity of the catalyst; B. Effect of total acidity of the
catalyst on the conversion of glycerol and selectivity to products
The data shows that the total acidity of the catalyst and the strength of medium acid sites
monotonously increased with increasing of HSiW loading. At low loading of HSiW below 10wt%,
there is essentially no effect on acidity. However, with a further increase in HSiW loading to
20wt%, the total acidity increased significantly. It is noted that the selectivity to 1-PO behaves in
parallel with the acidity and the strength of medium acid sites, while the selecitivity to 1,2-PD and
EG decreases with the loading level and is inversely proportional to the strength of medium acid
sites. It is suggested that total acid amount and medium acid site of the catalyst favor the formation
of 1-PO but disfavor 1,2-PD and EG.
94
At a low loading level of HSiW, although the dispersion is high, the direct interaction between the
surface and heteropolyacids are rather strong, causing sometimes decomposition of
heteropolyacids. NH3 adsorption shows that at low HSiW loading the strength of strong acid sites
is high (a shift toward higher temperature from 420oC to 480oC). The total acidity linearly increases
with the amount of HSiW loading. It shows the dependencies of the reactions with the loading
amount of HSiW on the catalysts.
The effect of different HSiW loading on catalyst surface area was investigated by N2 adsorption–
desorption isotherms. BET surface area was calculated by desorption isotherms and the result is
listed in Table 5-9. It is interesting to note that there is a slight increase in the surface area of the
catalyst from 17.9 to 20.9m2/g after HSiW was loaded onto 10Ni/Al2O3 suggesting that the pores
of alumina are not blocked by the HSiW. However, a further increase of HSiW loading does not
improve the surface area of the catalyst.
Table 5-9 BET surface area and total acidity of different HSiW loading catalysts
X-ray diffraction was carried out to identify the crystalline structure of the catalysts. The X-ray
patterns for different HSiW loading are shown in Fig. 5-17. Generally, bulk HSiW exhibits
characteristic crystalline peaks at 8o~10o, 20o~24o, 26o~28o, 32o~35o [158]. It can be seen that no
diffraction peaks corresponding to HSiW can be observed in the XRD pattern for 5 and 10wt %
HSiW supported 10Ni/Al2O3 catalyst, suggesting that HSiW was well dispersed on Al. As the
loading amount exceeds 10wt%, some characteristic crystalline peaks of HSiW gradually evolve.
This is a clear indication that large crystals of HSiW form which subsequently lower the HSiW
dispersion. It is believed that, heteropoly ions strongly interact with supports at the loading below
10%, while the bulk properties of these materials prevail at high loading. This can explain why the
HSiW,
wt %
SAA
m2/g
Weak acid site
mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid site
mmol/g
/(Temp.)
Total acid
amount, mmol/g
0 17.9 0.028/(175oC) 0.013/(350oC) - 0.041
5 20.9 0.022/(187oC) 0.024/(270oC) 0.027/(480oC) 0.073
10 20.9 0.029/(190oC) 0.035/(282oC) 0.042/(476oC) 0.106
20 21.1 0.154/(186oC) 0.191/(324oC) 0.149/(420oC) 0.494
30 21.2 0.232/(189oC) 0.396/(335oC) 0.168/(436oC) 0.796
95
acidity of the catalyst was low, being extremely low when the loading of HSiW is below 10wt%
and the acidity increases significantly at high loading.
Figure 5-17 XRD patterns for different HSiW loading
Summary
The variation of HSiW loading over the range of 0 to 30wt% influences both the glycerol
conversion and product distribution. The total acidity linearly increases with an increase in HSiW
loading. Acidity can promote the production of 1-PO but decreases the production of 1,2-PD and
EG. The loading of HSiW should be sufficiently high, i.e. 20wt % or higher) to promote the futher
hydrogenlolysis of 1,2-PD to 1-PO. 30wt% HSiW loading shows the highest activity in the
production of 1-PO.
5.3.2 Effect of different amounts Ni loading
It was found that 30wt% HSiW on a 10Ni/Al2O3 catalyst shows the highest activity in the
production of 1-PO. In this part of the research work the effect of Ni loading on the catalyst activity
of Ni/30HSiW/Al2O3 for the hydrogenolysis of glycerol was studied.
Experimental condition
The loading of Ni on the catalysts was varied from 0 to 15wt% to investigate the influence of Ni
loading on the catalytic activities of the yNi/30HSiW/Al2O3 catalysts. The experiment was
performed at 240oC, under 580PSI of H2 pressure using 2g of Ni supported 30HSiW/Al2O3
96
catalyst, 30g of glycerol (30wt%), 70g of DI water, 700RPM for 7hours. The catalysts were
reduced at 450oC for 5 hours.
Results and discussion
The conversions of the glycerol observed for different Ni loadings are shown in Fig. 5-18, 5-19
and the data are summarized in Table 5-9. The main products observed in the liquid phase were:
acetol, 1,2-PD, 1,3-PD, Acr, 1-PO and EG. Some other products (OP) such as methanol (MeOH),
ethanol (EtOH) were also obtained. However at low Ni loading of 0 and 1wt%, there are some
other light and heavy unidentified products also produced.
The data shows that, the variation of Ni loading over the range of 0 to 15wt% influences both the
glycerol conversion and product distribution. Among the catalysts, 5wt%Ni loading is most
effective for the conversion of glycerol to 1-PO. On increasing the Ni loading from 0 to 15wt%,
the conversion of glycerol and selectivity to Acr decreases gradually from 59% to 37.2% and
41.5% to 4.3% respectively; however the selectivity to different products is affected in a different
manner. While the selectivity to 1-PO went through a maximum of 86.8%, the selectivity to by-
products went through a minimum of 2.7% at 5wt % Ni loading.
Table 5-10 Effect of Ni loading on catalytic activity of the Ni/30HSiW/Al2O3
Ni
wt%
Acidity
mmol/g
Conv
%
Selectivity, %
1,3PD 1,2PD Ac EG 1-PO Acr OP
0 0.273 59.0
0.0 0.0 0.6 0.0 10.1 41.5
47.8*
1 1.297 53.4 0.0 0.0 1.3 0.0 41.7 42.0 15.0*
5 0.823 44.9 0.0 1.6 1.5 0.0 86.8 7.4 2.7
10 0.796 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.6
15 0.530 37.2 0.0 6.7 1.5 6.1 68.2 4.3 13.2
Reaction condition: yNi/30HSiW/Al2O3 (y= 0,1,5,10 and 15wt%) catalyst, 240ºC, 700RPM, 2g
catalyst, 30g of glycerol (30wt%), 70g of DI water and 580PSI of H2. *: By-products included
methanol, ethanol and unidentified light ad heavy
97
For the Ni-free catalyst (i.e. HSiW/Al2O3 catalyst) and a catalyst with 1wt % Ni loading, Acr is
dominant (around 42%), 1-PO was produced at low selectivity (10.1% and 41.7% respectively)
and no 1,2-PD was obtained. With increasing of Ni loading to 5wt%, the selectivity to 1-PO
significantly increases to 86.8%, whereas Acr decreased to a lower level of around 7% and 1,2-
PD appeared at 1.6% selectivity. However, further increase of the Ni loading led to a decrease in
selectivity to 1-PO, whereas the selectivity to 1,2-PD increases gradually to 6.7% with 15% Ni
loading, the selectivity to Acr continuously decreased to 4.3%. It should be noted that further
increase of Ni loading from 5wt% to 15wt% leads to an increase in the selectivity to other by-
products including methanol and ethanol. As can be seen from the Fig. 5-18, the selectivity of 1-
PO went through a maximum while the selectivity to by-products went through a minimum of at
5wt% Ni loading. The selectivity to Acr decreased but the selectivity to 1,2-PD increased. It is
believed that part of 1-PO came from the hydrogenation of acrolein that was produced from the
consecutive dehydration of glycerol which was also reported by Xufeng L. in 2014 [122].
Therefore, an increase in Ni loading can promote the hydrogenation of acrolein to 1-PO leading to
a decrease in the selectivity of acrolein but can also can cause a decrease in acidity of the catalyst.
This decrease in acidity can slow down the dehydration step that results in a decrease in conversion
of glycerol and suppresses further hydrogenolysis of 1,2-PD to 1-PO.
Figure 5-18 Effect of Ni loading on glycerol hydrogenolysis and products selectivity; Reaction
condition: yNi/30HSiW/Al2O3 (y= 0,1,5,10 and 15wt%) catalyst, 240ºC, 700RPM, 2g catalyst,
30g of glycerol (30wt%), 70g of DI water and 580 PSI of H2
98
Figure 5-19 Effect of Ni loading on glycerol hydrogenolysis and products selectivity as a function
of time. A) Glycerol Conversion; B,C,D,E,F) Selectivity of acetol, 1,2-PD, 1-PO, Acr., other
products, respectively. Reaction condition: yNi/30HSiW/Al2O3 (y=0, 1, 5, 10 and 15wt%)
catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and 580 PSI of
H2.
99
Figure 5-20 Pseudo-First-Order kinetic plots of effect of Ni loading on hydrogenolysis of glycerol
in the presence of Ni/30HSiW/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM, 2g catalyst,
30wt% (30g) aqueous glycerol and 580PSI H2
Characterization of catalysts
To examine surface acidity, NH3-TPD was performed. The TPD data was deconvoluted into 3
peaks (namely weak, medium and strong acid sites) using a Gaussian fitting method, the quantity
of acid sites of the catalysts is shown in Table 5-11 and Fig. 5-21 and was then correlated with the
catalytic activity of the catalysts.
Figure 5-21 NH3-TPD patterns for Ni loading
100
Table 5-11 BET surface are and acidities of different Ni loading catalysts
As can be seen, the total number of acidic sites decreases with increasing Ni content. A decrease
in acidity may possibly be due to the covering of acid sites by Ni or it can be suggested that this
behavior may result from direct anchoring on proton sites which forms blockage of acid channels
by Ni particles. It is important to note that Ni-free catalyst possesses low acidity (0.273mmol/g)
compared to that of the Ni supported catalyst. It maybe due to the fact that the Ni-promoted
catalysts in the presence of hydrogen increases the acidity that might be attributed to the formation
of water molecules during the reduction which could facilitate the formation of active Brønsted
acid sites which are considered to be the active reaction sites [83, 89-91]. However the strength
of acid sites does not follow this pattern. Among the catalysts, 5wt % Ni loading catalyst has its
weak and medium acid sites at its lowest strength; and there was a significant shift toward lower
temperature (shift of weak and medium acid sites from around 200oC to 95o C and 300oC to 236oC
respectively). This decrease in the strength of the acid site of the 5wt % Ni loading catalyst may
result in a proper balance between acid sites and metal sites so that an improvement in the activity
of the catalyst toward the production of 1-PO from glycerol.
BET surface area was calculated from desorption isotherms and the results are listed in Table 5-
10. As can be seen, the surface area increases with an increase in Ni loading. However, the increase
in surface area does not seem to affect either the catalyst activity or acidity.
To examine structural changes induced into its active phase, XRD was performed and the results
are shown in Fig. 5-22.
Ni
wt%
SAA
m2/g
Weak acid site
mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid site
mmol/g
/(Temp.)
Total acid
amount, mmol/g
0 17.7 0.031/(200oC) 0.205/(325oC) 0.038/(457oC) 0.273
1 15.2 0.214/(214oC) 0.273/(304oC) 0.811/(437oC) 1.297
5 17.9 0.084/(95oC) 0.538/(236oC) 0.201/(440oC) 0.823
10 21.2 0.232/(189oC) 0.396/(335oC) 0.168/(436oC) 0.796
15 22.2 0.106/(189oC) 0.277/(309oC) 0.148/(408oC) 0.530
101
Figure 5-22 XRD patterns for different Ni loading catalyst.
As can be seen from the XRD pattern, no diffraction peaks of NiO (2θ = 37.3o, 44.3 o and 62.9 o)
are observed for the Ni loadings of up to 5wt % suggesting that Ni was dispersed well; either in an
amorphous nature of Ni in the catalyst or that the size of Ni is smaller than the XRD detection
limit. Further increase in the Ni loadings to 15wt %, results in diffraction peakss attributed to the
NiO phase that can be observed and the intensities became stronger with a further increase of metal
loading. As the loading of Ni is increased the reason for the formation of diffraction peaks
attributed to the NiO might be due to the inhomogeneous distribution of the Ni species or the
particle becoming larger due to agglomeration when Ni was loaded at high levels. Furthermore the
intensities of the diffraction peaks attributed to the HSiW phase have been observed and the
intensities became weaker with an increase in metal loading. It is believed that in the case of
impregnated catalysts, the metal and the support are two separate phases and their interaction does
not lead to any major change in the support structure. As a result the diffraction peaks attributed
to the HSiW would decrease with increasing metal loading, since the added metal covers the pore
walls and eventually fills up the pores.
Summary
The variation of Ni loading over the range of 0 to 15wt% influences both the glycerol conversion
and product distribution. It is found that the catalyst having 5wt loading of Ni is the best catalyst
102
compared to the others; it can givethe highest selectivity to 1-PO, reducing the by-products as a
result of better dispersion of NiO on the surface of the catalyst. It is believed that part of 1-PO
came from the hydrogenation of acrolein that was produced from the consecutive dehydration of
glycerol. The total number of acidic sites and the acid strength was found to decrease with
increasing Ni content. A decrease in acidity may possibly be due to the covering of acid sites by
Ni or it can be suggested that this behavior may result from direct anchoring on proton sites and
from blockage of acid channels by Ni particles. To achieve good performance, catalysts must have
a proper balance between acid sites and metal sites.
5.3.3 Effect of catalyst preparation sequence on 10Ni/30HSiW/Al2O3 catalysts
The catalyst was prepared by impregnation of the components in sequence. So the active
components can be added in different sequences and this change in sequence may influence the
activity and selectivity of the catalyst. Here the effect of the preparation sequence was examined
by varying the order of component adding.
Experimental condition
The experiment was performed at 240oC under 580PSI of H2 pressure using 2g of
10Ni/30HSiW/Al2O3 catalyst, 30g of glycerol, 70g DI water, for 7hours. The catalyst was reduced
at 450oC for 5 hours.
Results and discussion
The effect of preparation sequences on the hydrogenolysis of glycerol are summarized in Table 5-
12 and depicted in the Fig. 5-23. The main products observed in the liquid phase were: acetol, 1,2-
PD, 1,3-PD, Acr, 1-PO and EG. Some other products (OP) such as methanol (MeOH), ethanol
(EtOH) were also obtained.
As can be seen from the data, the method of preparation shows little effect on the catalyst activity
in both the conversion of glycerol and product distribution. Among the catalysts, the one prepared
by the co-impregnation method is the most effective with high conversion of glycerol and the
selectivity of acrolein is low. When the component of HSiW was added first, the selectivity to 1-
PO and the conversion of glycerol was low but the selectivity to 1,2-PD was high compared to
other catalysts. It is suggested that there may be a decrease in acidity of the catalyst that can affect
103
the dehydration of glycerol and suppress further hydrogenoslysis of 1,2-PD to 1-PO. In contrast,
when Ni was loaded first, the selectivity to Acr was the highest.This may be due to the
hydrogenation of Acr to 1-PO slowdown (that may be caused by a decrease in Ni sites after loading
of HSiW on 10Ni/Al2O3 so lower acrolein exposure to Ni for hydrogenation). The catalysts
prepared by the co-impregnation method show the highest pseudo-first-order pseudo-first-order
rate constant compared to the other methods of preparation (Fig. 5-24).
Table 5-12 Effect of different sequence loading active components on product distribution
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. ** OP: By-products included methanol and ethanol
*HSiW first: The HSiW was added first then Ni was loaded onto 30HSiW/Al
*Ni first: The Ni was added first then HSiW was loaded onto 10Ni/Al
*Co-Imp: catalyst prepared by Co-Impregnation method
Sequence of
loading *
Acidity
mmol/g Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP**
*HSiW first 0.796 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.5
*Ni first 0.858 44.5 0.0 1.6 1.2 0.0 86.6 7.2 3.4
*Co-imp 1.264 47.6 0.0 2.2 1.0 0.0 86.9 4.8 5.1
104
Figure 5-23 Effect of preparation sequence loading active components on glycerol hydrogenolysis
and products selectivity as a function of time. A) Glycerol Conversion; B,C,D,E,F) Selectivity of
acetol, 1,2-PD, 1-PO, Acr., other products, respectively. Reaction condition:
10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI
water and 580 PSI of H2.
105
Figure 5-24 Pseudo-First-Order kinetic plots of effect of sequence adding components on
hydrogenolysis of glycerol in the presence of 10Ni/30HSiW/Al2O3 catalyst; Reaction condition:
240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and 580PSI H2
Characterization of catalysts
To examine surface acidity, NH3-TPD was performed. The TPD data was deconvoluted into 3
peaks (namely weak, medium and strong acid sites) using a Gaussian fitting method, the quantity
of acid sites of the catalysts was recorded and is shown in Table 5-13 and was then correlated with
the catalytic activity of the catalysts. Among the catalysts, the catalyst that is prepared by co-
impregnation has the highest acidity; however the strength of strong acid sites is the lowest
(427oC). The acidity of the catalyst significantly decreases when active sites were doped in
sequence. It is suggested that when the component was added in sequence the interaction between
component species and support may be stronger causing the catalyst to become harder to reduce
and affect the balance between the acid site and the metal site that leads to the reduction in total
acidity of the catalyst. When HSiW was added first, the decrease in acidity may be caused by the
covering of acid sites by Ni loading or it can be suggested that this behavior may result from direct
anchoring on proton sites and from blockage of acid channels by Ni particles.
Table 5-13 Total acidity of different sequence HSiW loading catalysts
Sequence
Weak acid
site mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid site
mmol/g
/(Temp.)
Total acid
amount, mmol/g
HSiW first 0.232/(189oC) 0.396/(335oC) 0.168/(436oC) 0.796
Ni first 0.228/(203oC) 0.428/(347oC) 0.202/(450oC) 0.858
Co-imp 0.367/(189oC) 0.421/(363oC) 0.475/(427oC) 1.264
106
Figure 5-25 NH3-TPD patterns for method preparation
X-ray diffraction was carried out to identify the crystalline structure of the catalysts. The X-ray
patterns for different sequence loading are shown in Fig. 5-26.
Figure 5-26 XRD patterns for method preparation
The XRD pattern of the pure support shows the peaks of alpha alumina. Compared with the XRD
pattern of Al, the peak intensity of the XRD pattern for all the catalysts diminishes. For all catalysts
the reflection of SiW is observed but the intensity is slightly different. The diffraction lines
corresponding to the reflections of HSiW (2θ= 220o~24o, 26o~28o, 32o~35o) can be observed in all
the XRD patterns of the catalyst, indicating that the layer formation of the HSiW phase at high
loading of 30% HSiW on the surface of the Al. It should be noted that the peak intensity of HSiW
107
for (HSiW first) catalyst is weaker than for the others, which implies that either (HSiW first) the
catalyst favors the dispersion of HSiW species on the surface of Al or the covering of HSiW by
additionof Ni. However, the peak intensity of the NiO species (2θ = 37.3o, 44.3 o and 62.9 o) is
similar for all catalysts
Aiming to understand the differences in reduction behavior coming from the preparation
methodologies, TPR studies were performed on all the catalyst samples and the result are shown
in Fig 5-27.
Figure 5-27 TPR patterns for sequence loading of component
As seen in Fig. 5-27, the TPR pattern of the all 3 catalysts shows H2 consumption peaks with a
maxima around 800◦C. The 2 lower temperature peaks between 300 and 500oC are attributed to
the reduction of highly dispersed NiO species that interact strongly with Al, and the higher
temperature peak to the reduction of larger NiO clusters, but also in contact with Al.
As for the catalyst that Ni was added first, a displacement of the maximum of the first peak to a
higher reduction temperature and is seen to overlap with the second peak and its height decreases,
indicating the formation of particles with less interaction with Al, and therefore is harder to reduce.
For the catalyst that is prepared by the co-impregnation method, the reduction peaks of Ni shift
toward lower temperature and overlap with the first peak, the reducibility of Ni is improved if the
catalyst is prepared bythe co-impregnation method.
108
Summary
Briefly, the sequence of adding the catalyst component during the preparation of catalyst can affect
the catalyst activity and the catalyst properties. Among these catalysts, the catalyst prepared by
co-impregnation is the most effective for the hydrogenolysis of glycerol to 1-PO with high
selectivity to 1-PO and low by-products prodution. Furthermore the catalyst prepared by the co-
impregnation method possesses the highest acidity among others.
5.4 Proposed reaction mechanism using heterogeneous metal catalysts
In order to elucidate the reaction sequence of glycerol hydrogenolysis and understand the
hydrogenolysis pathway of glycerol to lower alcohols the role of the intermediates 1,2-PD, 1,3-
PD, 1-PO over Ni/HSiW/Al was investigated under conditions similar to that of the hydrogenolysis
of glycerol and the results are presented in Table 5-14 and Fig 5-28.
Figure 5-28 Hydrogenolysis of glycerol and lower alcohols. Reaction condition:
10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI
water and 580PSI of H2, catalysts were reduced at 350oC for 5h.
The results show that with the same catalytic system the hydrogenolysis of 1,3-PD and 1-PO is not
as effective as the hydrogenolysis of glycerol and 1,2-PD. While the conversion of 1,3-PD and 1-
PO was low (26.4% and 8.5% respectivity), the conversion of glycerol and 1,2-PD was much
higher (71% and 98.1% respectively). Using different starting materials, 1-PO is always a major
109
product; however, the selectivity of 1-PO derived from 13-PD is low (only 77.4%) compared to 1-
PO derived either from glycerol (90%) or from 1,2-PD (90.8%). With respect to the formation of
ethylene glycol, it was obtained from glycerol hydrogenolysis; however, it was not detected in the
1,2-PD and 1,3-PD hydrogenolysis, suggesting that ethylene glycol was produced directly from
glycerol by a C–C bond cleavage reaction. In the reaction of glycerol and 1,2-PD, ethanol was
observed which can be formed via sequential hydrogenolysis of ethylene glycol or decomposition
of 1,2-PD. Since the conversion of 1-PO was much lower than that of 1,2-PD and 1,3-PD it can be
assumed that 1-PO is stable under the reaction conditions and can be considered as the final product
in the hydrogenolysis of glycerol using the catalyst 10Ni/30HSiW/Al2O3 under the reaction
conditions. In the hydrogenolysids of 1-PO using 10Ni/30HSiW/Al2O3 catalyst, 1-propanaldehyde
is produced as the major product. Using 10Ni/30HSiW/Al2O3 catalyst, it was clear that 1-PO was
formed mainly from the further hydrogenolysis of 1,2-PD and it is evident that ethylene glycol
was not obtained from 1,2-PD. It is thought that the pathway for the conversion of glycerol using
10Ni/30HSiW/Al2O3 catalyst would involve glycerol dehydration to acetol or 3-HPA on acid sites,
followed by hydrogenation of acetol or 3-HPA on metal sites to produce 1,2-PD or 1,3PD
respectively. Then further hydrogenolysis of 1,2-PD or 1,3-PD will produce 1-PO. Therefore the
role of Ni and HSiW for hydrogenation and dehydration respectively in the hydrogenolysis of
glycerol was studied in this respect.
Table 5-14 Hydrogenolysis of different starting materials using 10Ni/30HSiW/Al2O3 catalyst
*a: Unreduced catalyst
*b: HSiW/Al catalyst
*c: Ni/Al catalyst
1 2 3 4 5 6 7 8
Reactant Glycerol Glycerol Glycerola* Glycerolb Glycerolc* 12PD 13PD 1PO
Gas Nitrogen Hydrogen
Conversion 22.9 72.3 71.6 69.0 56.3 98.1 26.4 8.5
Selectivity
Acetol 17.3 0.6 1.1 0.6 0.5 - - -
1,2PD - 1.1 - - 20.4 - - -
1-PO 13.9 91.2 67.6 10.1 13.4 90.8 77.4 -
EG - - - - 11.8 - - -
110
MeOH - 1.3 1.4 - 2.4 - - -
EtOH 4.9 2.7 1.6 - 51.5 2.1 15 20.7
Acr 13.4 2.9 25.9 39.4 - - 0.8 -
Propanal - - - - - 4.5 - 79.3
UIP 50.5** 0.2* 2.4** 49.9** - 2.6* 6.8* -
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2, catalysts were reduced at 350oC for 5h.
*UIP: unidentified light products; **UIP: unidentified light and heavy products
To explore a bifunctional metal-acid catalysed pathway for the hydrogenolysis of glycerol in a
batch autoclave, first the dehydration of glycerol on 10Ni/30HSiW/Al2O3 catalyst was tested under
the same conditions applied to glycerol hydrogenolysis without addition of H2 as a reactant for the
hydrogenation step (N2 was used instead of H2) (Table 5-14, colume 1). Without H2, the reaction
was slow, yielding acetol and acrolein in moderate selectivity (12.5% and 12% respectively) and
selectivity to 1-PO is low (15.6%) at only 24.9% conversion of glycerol compared to the reaction
with H2 in which the conversion of glycerol and selectivity to 1-PO increase significantly to 72.7%
and 90% respectively (column 2). Since metal is required for hydrogenation, the non-reduced
catalyst was tested to elucidate the role of the metal (Table 5-14, colume 3). The data show that
without reducing, the activity of the catalyst is similar to the reduced catalyst with respect to
glycerol conversion; however, the product distribution is influenced significantly. Compared to
the reduced catalyst (column 2) the selectivity to 1-PO decreased from 90% to 67.6%; however,
the selectivity of acrolein increased from 2.9% to 25.9%. The result show that the unreduced
catalyst lost its activity or has hydrogenation activity severely reduced for the hydrogenation of
acrolein to 1-PO.
Then the dehydration of glycerol using the catalyst without Ni addition was tested (Table 5-14,
colume 4). As can be seen from the Table 5-14, the catalyst affects slightly the catalyst activity in
terms of the conversion of glycerol which reaches 69%; however, it affects the product distribution
significantly. The selectivity to 1-PO significantly decreases from 90% to around 10% whereas
the selectivity to acrolein increases from 2.9% to 39.4%. This again suggests that Ni is required to
hydrogenate acrolein to 1-PO. Then the role of Ni was studied using only a metal of Ni supported
alumina (Table 5-14, colume 5). The data shows that 1,2-PD is produced as a major desired product
with a selectivity of 20.4% and ethanol as a main by-product whereas 1-PO was produced in low
111
selectivity of 13.4%. The low 1-PO selectivity is expected to be due to lack of acidity for further
hydrogenolysis of 1,2-PD to 1-PO, and Ni alone promotes the rupture of C-C bonds to produce
ethanol. These results support the bifunctional mechanism for glycerol hydrogenolysis over the
10Ni/30HSiW/Al2O3 catalyst.
It is well-known from the literature that acid catalysts can be used to carry out dehydration of
alcohols in which the alcohol can be protonated by a Brønsted acid. Acidic sites can donate a
proton to the reactant molecule and form a carbocation transition state that is the primary driver of
the activity and selectivity of the reaction. In the dehydration of the alcohol, the acid catalyst tends
to favor removal of hydroxyl groups from carbons that form a more stable carbocation. Primary
alcohols are generally less reactive than the corresponding secondary alcohols due to the smaller
electron-releasing inductive effect of one alkyl group as compared to two alkyl groups while the
secondary carbocation is more stable than the primary carbocation [159,160].
In glycerol hydrogenolysis, the first step involves an initial protonation of the hydroxyl group that
leads to the formation of a carbocation and water [161,162]. The initial acid catalyzed dehydration
is the selectivity controlling step. If the primary hydroxyl group is eliminated 1,2-PD will be
obtained; if the secondary alcohol is eliminated then 1,3-PD will form. The dehydration of a
primary alcohol produces acetol that is thermodynamically more stable than the dehydration of a
secondary alcohol to form 3-HPA. Although dehydration of a secondary alcohol will occur via a
relatively more stable intermediate secondary carbocation [105,163], the reaction is kinetically
controlled [164,165]. This is likely due to the steric hindrance of the two primary alcohol
functional groups in the glycerol.
Acetol is formed via the elimination of the primary hydroxyl group; while the elimination of
secondary hydroxyls will produce 3-HPA. Although 3-HPA is more reactive compared to acetol
[59,166], it was not observed as an intermediate in the liquid phase under our reaction conditions.
The hydrogen activated on the metal facilitates the hydrogenation of acetol or 3-HPA to release
1,2-PD or 1,3-PD respectively. However, the dehydration of 3-HPA on the acid sites to form
acrolein is very facile [204-208], therefore it is not easy to obtain 1,3-PD unless the hydrogenation
reaction can be facilitated by a very active hydrogenation environment .
112
Further hydrogenolysis of propanediols will form 1-PO. Again the protonation of the hydroxyl
groups of propanediols can produce reactive carbocation intermediates. A dehydration reaction of
propanediols requires protonation of the alcohol group on the primary or secondary carbon to form
primary or secondary carbocation ions respectively [172]. 1,2-PD having the secondary hydroxyl
group can be easily dehydrated to produce 1-PO. Dehydration of 1,3-PD also leads to 1-PO
although it is expected to be less facile as the dehydration produces the less stable primary
carbocation. The pseudo first order rate constants shown in Chapter 4 (Fig 4-5) shows the rate
constant for the conversion of 1,2-PD is the highest, followed by glycerol. The conversion of 1,3-
PD is slower than the glycerol conversion while the conversion of 1-PO is the slowest. The
conversion of 1,2-PD and 1,3-PD shows the rate constants for the conversion of 1,2-PD is 15
times faster than for 1,3-PD. These rate constants provide important information on the proposed
reaction pathway for glycerol hydrogenolysis and also the product selectivity.
Based on the literature review [50, 59, 64, 108, 116] and our experimental results, we propose the
following detailed mechanism to explain the formation of the 1-PO in the glycerol hydrogenolysis
over the 10Ni30HSiW/Al2O3 catalyst (Scheme 5-1). The intermediate products that are formed
from glycerol are acetol, 3-hydroxypropylaldehyde ( 3-HPA) , 1,2-PD, 1,3-PD and acrolein. 3-
HPA and acetol are formed via the dehydration on acid sites of the hydroxyl group at the secondary
and primary carbon atoms. While the overdehydration of 3-HPA forms acrolein following by the
hydrogenation to form 1-PO; the hydrogenation of acetol or 3-HPA leads to 1,2-PD or 1,3-PD
formation with further hydrogenolysis of 1,2-PD or 1,3-PD to give 1-PO. Since 3-HPA is more
reactive compared to acetol [59, 166], it was not observed as an intermediate in the liquid phase.
Scheme 5-1. Proposed mechanism for hydrogenolysis of glycerol via bifunctional metal-acid
catalysis.
113
From the mechanism proposed, we suggest that the main route for the formation of 1-PO from
glycerol is via either the hydrogenation of acrolein or further hydrogenolysis of 1,2-PD (and
1,3PD) where 1,2-PD (and 1,3-PD) and acrolein are the intermediates in the formation of 1-PO
from glycerol. In the absence of hydrogen, acetol and acrolein were the major products. Therefore
hydrogen is required for the next step of hydrogenation of theses intermediates to form 1-PO.
5.5 Leaching and recyclability of catalyst
The solid bifunctional catalyst used in the reaction can be separated from the reaction mixture as
it is heterogeneous. However whether the catalyst suffers from leaching and if it could be reused
for the same purpose are one of the aspects that must be explored.
The leaching of catalyst can be measured by using a hot filtration method. The catalyst was filtered
out from the reaction mixture at the stage of 50% conversion. If reaction further proceed, that
means leaching of catalyst happened. On other hand, if there is no further progress in the reaction
that indicates either there is no leaching or the leaching of component is not sufficient to keep the
reaction proceeding. To study the leaching of HSiW supported catalyst, the catalyst was filtrated
from the liquid after 7h of experiment. Then the liquid was placed back into the autoclave. The
experiment was carried out for 6h to test for catalyst leaching. The results are shown in Table 5-
15.
Table 5-15 Continuing reaction after filtering the 10Ni/30HSiW/Al2O3 catalyst
Leaching CGL
mol/l
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO OP*
Before testing 3.111 0.0 2.9 1.21 0.0 80.9 14.9
After testing of 6h 3.088 0.0 1.6 1.16 0.0 78.4 18.9
OP*: methanol, ethanol and light unidentified products
As can be seen from the Table 5-15, there is a slight decrease in the concentration of glycerol and
selectivity to 1-PO and an increase in OP which suggest that the leaching is not significant or the
components that leached out from catalyst are essentially catalytically inactive for the reaction.
114
To confirm if the leaching of catalyst affects the catalyst activity, the recylibilty of the catalyst was
studied. To study the recyclability of the HSiW supported catalyst 3 type of catalysts that were
reduced at different temperature (350oC, 400oC and 450oC) were used and recycled. For each type
of catalyst, two experiments were carried out using 2g of catalyst and then the catalysts were
recovered and reused one time.
The results were presented in the Table 5-16. It is shown that the activity and acidity of the catalyst
reduced at 350oC and 400oC decreases after recycling. For both catalysts the conversion of glycerol
shows a decrease of around 10% and there is a change in the distribution of products. The
selectivity to 1-PO decreases while the selectivity to 1,2-PD, EG and by-products increases. It is
belived that the loss in activity and acidity may be a result of leaching of HSiW. As a result the
basisity of the catalyst may increase leading to an increase in selectivity to EG. It is unexpected
that the catalyst reduced at 450oC showed an increase in activity with repect to the conversion of
glycerol and selectivity to 1-PO, an increase in selectivity to EG was still observed. It is thought
that after the catalyst involved in the hydrogenolyis of glycerol in water media, water may be added
to recover the heteropoly acid so the catalytic activity was increased.
Table 5-16 10Ni/30HSiW/Al2O3 catalyst recycling study
Red.
Temp Catal
Conv
mol%
Selectivity, mol%
13PD 12PD Acetol EG 1-PO OP
350 Fresh 72.3 0.0 1.1 0.6 0.0 91.7 6.6
Reused 69.6 0.0 1.8 0.5 2.7 87.7 9.9
400 Fresh 67.4 0.0 1.7 0.6 0.0 91.2 6.5
Reused 57.4 0.0 8.3 0.7 5.8 71.9 13.3
450 Fresh 43.8 0.0 2.9 1.2 0.0 80.9 14.9
Reused 63.1 0.0 3.6 0.7 2.7 79 14.1
115
5.6 Conclusions
The catalyst of 10/Ni/30HSiW/Al2O3 was prepared using the impregnation method and a
parametric study was performed to understand the effect of different factors such as catalyst
loading, reaction temperature, and hydrogen pressure.
It is found that the hydrogenlysis of glycerol is chemically controlled at a stirring speed of 500RPM
which is sufficient to further hydrogenolyis of 1,2-PD to 1-PO but not increase the side reactions
to produce by products.
The conversion of glycerol is inversely related to the hydrogen pressure due to most likely to the
reduction of W6+ to W5+or 4+ and a reduction in acidity. However the high H2 pressure is necessary
to suppress the undesired dehydration or a side reactions and decrease the undesired products.
Optimal operating H2 pressures are required to obtain a high yield of 1-PO.
Dilute feed solutions results in an increase of selectivity to 1-PO but lower the conversions of
glycerol. Increasing the glycerol concentration (decreasing the initial water content) decreased the
selectivity to 1-PO but the selectivity to 1,2-PD and acrolein increased. Optimal glycerol feed
concentration is required to obtained high yield of 1-PO.
Conversion increased with catalyst loading, but selectivity to 1-PO reached a maximum of 92.7%
at 4.5% loading. It is thought that high catalyst loadings may increase the decomposition of the
product or promote side reactions. Optimal catalyst loading is required to obtain a high yield of 1-
PO.
Increasing temperature may promote further hydrogenolsis of 1,2-PD to 1-PO. However excessive
heat may cause the degradation of 1-PO to other products.
The total acidity linearly increases with an increase in HSiW loading. Acidity favors 1-PO while
basicity favors 1,2-PD and EG. The loading of HSiW should be 20% or higher to promote the
futher hydrogenlolysis of 1,2-PD to 1-PO.
The catalyst having 5% loading of Ni is the best catalyst compared to others; it can give the highest
selectivity to 1-PO, and reduce the by-products as a result of better dispersion of NiO on the surface
of the catalyst. It is believed that part of 1-PO came from the hydrogenation of acrolein that was
116
produced from the consecutive dehydration of glycerol. The total number of acidic sites and the
acid strength was found to decrease with increasing Ni content. A decrease in acidity may possibly
be due to the covering of acid sites by Ni or it can be suggested that this behavior may result from
direct anchoring on the proton sites and from blockage of acid channels by Ni particles.
The sequence of adding the catalyst component during the preparation of the catalyst can affect
the catalyst activity and the catalyst properties. Among these catalysts, the catalyst prepared by
co-impregnation is the best for the hydrogenolysis of glycerol to 1-PO with high selectivity to 1-
PO and low by-products are produced. Furthermore the catalyst prepared by the co-impregnation
method possesses the highest acidity and the easy reducibility of Ni.
The mechanism proposed suggests that the main route for the formation of 1-PO from glycerol is
via either the hydrogenation of acrolein or further hydrogenolysis of 1,2-PD (and 1,3-PD) where
1,2-PD (and 1,3-PD) and acrolein are the intermediates in the formation of 1-PO from glycerol. In
the absence of hydrogen; acetol and acrolein were the main products which suggested that
hydrogen is nessessary for the next step of hydrogenation of intermediates to produce desired
products.
Although 10Ni/30HSiW/Al2O3 catalyst shows a good activity for the production of 1-PO from
glycerol; the leaching of the catalyst is a concern and should be addressed in future studies.
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Chapter Six
Keggin type Heteropolyacid supported catalyst for hydrogenolysis of
glycerol to 1-Propanol
Heteropolyacids (HPAs) present several advantages as catalysts that make them economically and
environmentally attractive. [66,167]. Among the HPAs, the best known of these structures is the
Keggin‒type heteropolyacids, HPAs which are very strong BrØnsted acids; stronger than common
irorganic acids (HCl, H2SO4…) and are even sometimes classified as super acids [168,169].
However their acid properties can be tuned by modifying their compositions.
From the previous section, the hydrogenolyis of glycerol over silicotungstic acid (HSiW), one of
most well−known Keggin type HPAs structures, results in high selectivity to 1-PO at moderate
glycerol conversion. It is found that the acidity of HSiW is crucial to providing high selectivity to
1-PO since it is required for further hydrogenolysis of 1,2-PD to 1-PO. In this chapter the effect of
different Keggin-type heteropolyacids, the effect of Cs, the effect of treatment temperature and the
effect of support were studied for the hydrogenolysis of glycerol to other chemicals in particular
the conversion to 1-PO will be investigated as these factors can tune the acidity of the catalyst.
The catalyst characterizations were carried out to study the relationship between the catalyst
physicochemical properties and the catalytic activities. The characterization techniques including
NH3 temperature programmed desorption (TPD), temperature programmed reduction (TPR),
thermogravimetric analysis (TGA), X-Ray diffraction (XRD), Fourier transform infrared (FTIR)
and Brunauer–Emmett–Teller (BET) surface area analysis. The characterization results were
analyzed according to the experimental results.
6.1 Efficient hydrogenolysis catalysts based on Keggin polyoxometalates
Heteropoly acids (HPAs) with the Keggin structure that are well-known as environmentally
friendly and economically viable solid acids [170] have been used for the upgrading of glycerol to
other chemicals. Different forms of HPAs are used as catalysts, among them silicotungsticacid
(HSiW), phosphotungstaticacid (HPW) and phosphomolybdicacid (HPMo) as a consequence of
their high catalytic activity in the selective dehydration of glycerol [72, 73, 76, 85, 142, 171]. The
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acidity of the HPAs strongly depends on the nature of the addenda atoms. For example, the HPAs
containing W are more acidic than those containing Mo. Since the Mo-O terminal bound is more
polarizable than the W-O terminal bound. The O atoms linked to Mo atoms are negatively charged
and protons are less mobile in this case. Hernández-Cortez J.G.et al. [172] studied the dehydration
of secondary alcohols using HPAs supported on different solids and it was found that the
interaction between supports and HPAs affects the physicochemical properties of the prepared
catalysts. The Keggin structure was retained when they were supported. The product distribution
depends on different type of HPAs (HPMo, HSiW and HPW) due to the difference in acid and
base properties. In 2005 Thomas stated that the acidity of HPW can be changed by high
temperature variation and HPW losses its protons at a lower temperature than HSiW [173].
Although work has been done to study different type of HPAs (HPMo, HSiW and HPW) for the
dehydration of glycerol [73, 76], hardly any work has done on the direct conversion of glycerol to
1-PO using different HPAs supported catalyst.
Thus in this work, Keggin-type heteropolyacids, including phosphotungstic acid (HPW),
phosphomolybdic acid (HPMo) and silicotungstic acid (HSiW) , and nickel were loaded onto
alumina for the hydrogenolysis of glycerol. The aim was to investigate the effect of HPAs
composition on the catalytic activity, the role of acidity of the catalyst and to follow the effect of
temperature treatment of the catalyst on the Keggin structure and surface acidity properties of the
catalyst during the course of the hydrogenolysis reaction. For this study, the catalysts were
prepared via the sequential impregnation method. The properties of the prepared catalysts were
characterized using TPD, XRD, FTIR techniques. Activity tests were performed in a 300ml
Hastelloy Parr batch autoclave using 30g glycerol, 70g DI water, 580PSI Hydrogen at 240oC and
2g catalysts. Prior to each experiment, the catalyst was reduced in a quartz tubular reactor for 5
hours. The main products observed in the liquid phase were: Acetol, 1,2-Propanediol (1,2-PD),
1,3-Propanediol (1,3-PD), 1-Propanol (1-PO) and ethylene glycol (EG). Some other products such
as methanol, ethanol, acrolein were also obtained and named as other products (O.P.).
Experimental condition
The effect of different HPAs was examined at constant reaction conditions. The experiment was
performed in a 300ml Hastelloy Parr batch autoclave at 240oC under 580PSI of H2 pressure using
2g of 10Ni/30HSiW/Al2O3 catalyst, 30wt% staring materials (30g of glycerol), for 7hours. Two
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catalysts reduced at different temperature were studied. One was reduced at 350oC and another
was reduced at 450oC for 5 hours.
Results and discussion
The effect of heteroatom substitution on the catalytic activity of the HPA catalysts for the
hydrogenolysis of glycerol to other chemcials was examined at different reduction temperature.
The results after reaction for 7 h are shown in Table 6-1. The main products observed in the liquid
phase were: acetol, 1,2-PD, 1,3-PD, Acr, 1-PO and EG. Some other products (OP) such as
methanol (MeOH), ethanol (EtOH) were also obtained.
Table 6-1 Effect of different HPAs supported 10Ni/Al2O3 catalyst on the conversion of glycerol
and the distribution to products in the hydrogenolysis of glycerol
Catalyst Red.
temp oC
Conv
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP*
10Ni/30HSiW/Al2O3
350 72.3 0.0 1.1 0.6 0.0 91.7 3.3 3.3
450 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.5
10Ni/30HPW/Al2O3
350 51.1 0.0 2.9 0.7 2.2 87.7 3.2 3.3
450 48.9 0.0 6.1 1.0 3.7 80.3 3.3 5.7
10Ni/30HPMo/Al2O3
350 1.0 0.0 10.7 35.2 0.0 54.1 0.0 0.0
450 1.0 0.0 10.1 36.5 0.0 53.4 0.0 0.0
Reaction condition: 10Ni/30HPAs/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. *OP: By-products included methanol and ethanol
The data shows that the activity of the HPA supported catalyst is affected by reduction temperature.
As can be seen from Table 6 -1 at a low reduction temperature of 350oC the catalyst activity of
HPAs is in the order of HSiW >HPW >HPMo. Over a HSiW supported catalyst the selectivity to
1-PO reached 90% at 72% conversion of glycerol while the selectivity of 1,2-PD was low at 1.1%.
Compared to HSiW, other supported HPAs catalysts showed lower activity towards glycerol
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conversion and selectivity to 1-PO. While the HSiW supported catalyst achieved the best catalytic
performance in terms of glycerol conversion and selectivity to 1-PO, the HPMo supported catalyst
is inactive. In all cases, 1-PO is produced as the main product and acrolein, methanol, ethanol are
the by-products of the reaction.
Figure 6-1 Concentration profiles of different HPAs supported 10Ni/Al2O3 catalyst at different
reduction temperature at 350 and 450oC. Reaction condition: 30g of glycerol (30wt%), 70g of DI
water, 580PSI of H2, 240oC, 700RPM, 2g catalyst reduced at 350oC and 450oC, 7 hours
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Figure 6-2 Pseudo-First-Order kinetic plots of effect of HPAs on hydrogenolysis of glycerol in
the presence of 10Ni/30HPA/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM, 2g catalyst,
30g of glycerol (30wt%), 70g of DI water and 580PSI H2
When the reduction temperature increases to 450oC, glycerol conversion decreased to low values
of 43% over HSiW supported catalyst. Accordingly, selectivity to 1-PO slightly decreased. While
the conversion of glycerol remained similar at around 50% over the HPW supported catalyst; the
selectivity to 1-PO also slightly decreased. In all cases, higher reduction temperature reduces the
activity of the catalyst but not the selectivity, with the exception of the HPMo supported catalyst
that is inactive already at 350oC treatment.
Characterization of catalysts
The catalysts were characterized by different techniques
The relationship between catalytic activity and catalyst properties in particular the acid
concentration of the catalysts was studied using different techniques.
The NH3-TPD was performed from 50 to 750◦C to study the acidic properties on the catalyst
surface in order to elucidate the catalytic activity of catalysts, and thus, to find a comprehensive
correlation between catalytic activity and acid property of the HPA catalysts. The TPD data was
deconvoluted into 3 peaks (namely weak, medium and strong acid sites) using a Gaussian fitting
method. Two different NH3-TPD profiles of the catalysts reduced at 350oC and 450oC with
different Keggin-type heteropolyacids loaded are shown in Fig. 6-3 and Fig. 6-4. The total acidity
of the catalysts is recorded in Table 6-2 and was then correlated with the catalytic activity of HPA
catalysts.
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Figure 6-3 NH3-TPD patterns for different HPAs reduced at 350 and 450oC
Figure 6-4 Total acidity amount for different HPAs reduced at 350 and 450oC
123
Table 6-2 Effect of different HPAs supported 10Ni/Al2O3 catalyst and reduction temperature on
acidity and catalyst performance
Qualitatively, a positive correlation is observed between glycerol conversion and acid
concentration over HSiW supported catalyst. However, the correlations are not observed for the
other 2 catalysts, i.e. HPW and HPMo.
As can be seen from Fig. 6-3, Fig 6-4 and Table 6-2, for both reduction temperatures of 350 and
450oC, the HSiW supported catalyst shows the highest total acid amount while the HPMo
supported catalyst possesses the lowest total acid amount among all catalysts. The total acidity is
in the order of 10Ni/30HSiW/Al2O3 >10Ni/30HPW/Al2O3> 10Ni/30HPMo/Al2O3>10Ni/Al2O3
and the total acidity decreases as the reduction temperature increases (Fig. 6-4). Whithout HPAs,
it was found that the acidity of 10Ni/Al2O3 was low; only 2 broad small peaks of weak and medium
acidity were observed at around 200oC and 350oC. After heteropolyacids loading, all curves are
composed of overlapped 3-peaks between 100 and 600◦C, indicating the presence of 3 acid centers
with different strengths. These results illustrated that the Keggin-type heteropolyacids loading
increases the acidity of the catalysts, offering acid sites for catalysis. Different kinds of Ni-
HPAs/Al catalysts provide a difference in the acidity. It can be seen from Table 6-2 that the order
Catalyst
Red.
temp, oC
k, s-1
E-05
Weak acid site
/(Temp.)
Medium acid
site /(Temp.)
Strong acid
site/(Temp.)
Total acid
amount,
mmol/g
Conv.
mol %
Ni/Al2O3
350 2.3 0.027(185oC) 0.016/(372oC) - 0.043 40.4
450 3.1 0.028/(175oC) 0.013/(350oC) - 0.041 51.6
Ni/HSiW/Al2O3
350 5.5 0.180/ (182oC) 0.504/ (335oC) 0.196/ (441oC) 0.880 72.3
450 2.4 0.232/(189oC) 0.396/(335oC) 0.168/(436oC) 0.796 43.8
Ni/HPW/Al2O3
350 3.21 0.090/(185oC) 0.365/(338oC) 0.120/(438oC) 0.575 51.2
450 3.06 0.020/(180oC) 0.226/(340oC) 0.029/(511oC) 0.275 48.9
Ni//HPMo/Al2O3
350 0.039 0.040/(167oC) 0.135/(234oC) 0.108/(426oC) 0.283 1.0
450 0.034 0.068/(207oC) 0.043/(292oC) 0.034/(536oC) 0.145 1.0
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of acidity amount is: HSiW > HPW > HPMo. It is noticeable that the performace in catalytic
activity is consistent with the trend of the amount of acidity of these HPA catalysts. When the
catalysts were reduced at a low temperature of 350oC, the TPD pattern of HSiW and HPW is
almost similar, illustrating that this low reduction temperature does not affect the acidity of the
these two HPAs catalysts. However, there was a reduction in the proton content for all of the
heteropolyacids when the catalyst was reduced at 450oC. HPW and HPMo lost their acidity much
more readily than HSiW. While the TPD pattern over HSiW supported catalyst was similar at both
reduction temperature, new patterns of the acidity for HPW and HPMo were observed at a high
reduction temperature - there was a shift toward higher temperature of strong acid sites with
increasing reduction temperature.
These results suggest that the acidity of Keggin-type heteropolyacids was affected by the high
temperature, that the structures of the heteropolyacids were probably changed or damaged. The
decomposition of the crystal structure upon heating at high temperature leads to a loss in acidity
and the removal of protonated water under heat treatment which may account for the acidity loss,
mainly decreasing Brønsted acidity.
It is interesting to note that the activities of the HSiW and HPW catalysts reduced at 450oC have
similar activity as they also have similar acidity in medium acid site as can be seen from Table 6-
2. It is suggested that medium acid sites affect to some extent the activity of the catalyst.
The catalysts were characterized using XRD to explore the crystal phases and to check possible
HPAs support interactions giving rise to distortion of the HPAs structure of the catalysts. The XRD
pattern of the alumina support, Ni supported alumina and the supported HPAs catalyst is shown in
Fig. 6-5.
Generally, bulk HSiW exhibits characteristic crystalline peaks at 8o~10o, 20o~24o, 26o~28o,
32o~35o [158]. As can be seen for the HSiW and HPW catalysts some minor characteristics
crystalline peaks of HSiW (20o~24o, 26o~28o) can be observed but no significant changes in the
diffraction patterns occurred compared to the Ni/Al catalyst, indicating that there is no change in
the structure. However the XRD pattern of the HPMo supported catalyst is different from the other
two catalysts. There are diffraction peaks that do not coincide with the diffraction of HPMo but
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resemble orthorhombic MoO3. This can be explained by considering the decomposition of HPMo
into MoO3 species under preparation treatment.
Figure 6-5 XRD patterns for different HPAs calcined at 350oC
Infrared spectra are also an informative fingerprint of the Keggin heteropoly cage structure.
Therefore the prepared catalysts were analyzed by FTIR in order to confirm the structural integrity
of the Keggin unit of these catalysts. All the catalysts were calcinated at 350oC prior to analysis.
The FTIR spectra of the catalysts are presented in Fig. 6-6.
Figure 6-6 FTIR patterns for different HPAs calcined at 350oC
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It is shown that the evidence for the retention of the Keggin ion structure on the surface of HSiW
and HPW supported catalysts was provided; however the HPMo supported catalyst was already
decomposed under the preparation condition at 350oC of calcination. The fingerprint bands of the
HSiW Keggin anion appeared at 978, 915, and 798 cm−1, which could be assigned to the typical
antisymmetric stretching vibrations of W=O, Si–O, and W–Oe–W [145]. This indicated that the
Keggin phase remains intact for the HSiW supported catalyst. For the supported HPW catalyst, 3
bands of HPW appear around 1079, 983 and 810 cm−1 that can be assigned to the typical
antisymmetrical stretching vibrations of P–O, W=O, and W–O–W [174]. These spectra exhibit
similar bands for the structure of the PW12O403- anion also suggesting that HPW in the catalyst still
retains the Keggin structure. However, the FTIR spectra of HPMo supported catalyst was different
from HSiW and HPW. The spectra of Keggin ion was not observed for HPMo sample but only the
spectra of orthorhombic α-MoO36 appeared. This confirmed that the decomposition of HPMo to
MoO3 occurred at 350oC. It is believed that the decomposition of HPMo into MoO3 at higher
temperatures is responsible for the decrease in catalytic performance. The Keggin structure of
HSiW is rather stable and is the best candidate for 1-PO production
Summary
The activation process is associated with structural changes and these structural changes match
with those that occur during thermal treatment – in fact, thermal stability is known to be extremely
important for catalyst stability [175,176]. The effect of reduction temperature on the activity of
different HPA supported catalyst was not the same for all catalysts. Under our reaction conditions,
the HSiW supported catalyst seems to be more stable than other catalysts up until a treatment
temperature of 450oC and is the best candidate for 1-PO production. The decomposition of HPMo
already occurred at 350oC of treatment. The decomposition of HPMo into MoO3 is likely to be
responsible for the inactivity of the catalyst for glycerol conversion.
6.2 The effect of thermal treatment on activity and structure of
10Ni/30HSiW/Al2O3 catalyst
It has been shown that the performance of a heterogeneous catalyst not only depends on the
intrinsic catalyst components but also on its texture and stability. One of the most important factors
affectings the texture and activity of a catalyst is the proper choice of the activation step. HPAs
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have proved their remarkable and unique simultaneous acid and redox properties but their rapid
degradation at high temperature by decomposition is still a major drawback [177]. The stability of
these compounds is thus a critical parameter that has been extensively studied. The effect of
temperature on the catalyst structure was studied. However, the effect of temperature on the HPAs
supported catalyst activity for the conversion of glycerol is rarely studied. In 2014 Liu et. al. [171]
studied the effect of calcined temperature on the structural evolution of Al2O3 supported HSiW
and the catalytic performance during glycerol conversion to acrolein. The decomposition of
supported HSiW crystal structure and the degradation of Keggin unit occured after calcination of
HSiW/Al2O3 at 350 and 450◦C, but to a small extent. However the Keggin structure was
decomposed totally at 550 and 650◦C. One important property of HPAs; is their thermal stability,
is discussed in this section. The effect of the calcination temperature and reduction temperature of
the HSiW on the physico-chemical properties of supported Ni catalysts will be investigated. The
change of the acidity with the increasing temperature and the performance of the catalysts in the
hydrogenolysis of glycerol will be investigated.
6.2.1 The effect of calcined temperature
Although HPAs showed high activity for glycerol dehydration, the tendency to decompose under
thermal treatments always leads to a loss of active sites and deactivation [72-75]. It is well known
that calcination is basically thermal decomposition with air at the decomposition temperature.
During this process, the active centers are usually generated, where calcination of supported HPA
catalysts below the decomposition temperature would favor the creation of proper interaction
between the heteropolyanions and the support surface, improving the stability of HPAs as solid
acid catalysts. However, if the temperature is further increased, the Keggin structure can be
gradually decomposed. For HSiW supported catalyst, calcination is generally carried out at about
350°C under atmospheric pressure to remove the precursor decomposition products efficiently.
The upper level of temperature can be put as the limit where all the acidic properties are lost.
Kozhevnikov [170] proposed a mechanism related to losses during heating. The process consists
of three steps of which the first is vaporization of water at 100°C. At 200°C and 450-470°C, water
molecules bonded to the acidic protons and the remaining protons are removed respectively. At
temperatures higher than 600°C, the component is totally converted to P2O5 and WO3 which shows
no acidic property. Martin et al. studied the decomposition behaviors of HSiW and HPMo HPAs
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using DTA technique [76]. The loss of water, the interaction with the support and the formation
of new species were observed. Ezzat Rafiee et al. [178] synthesized the green core nanorod catalyst
for the C-N coupling reactions at room temperature. The effect of calcination temperature at 100,
150, 200, 250, and 300oC was investigated and it is found that the catalyst calcined at 150oC was
observed to have very low leaching of the HPW in the heterogeneous catalytic system. This
catalyst was easily recyclable with slight loss of catalytic activity. Devassy prepared the catalysts
with different HSiW loadings and calcination temperatures (600–850◦C) for veratrole benzoylation
[179]. It is found that 15% HSiW on zirconia calcined at 750◦C that was highly dispersed on the
support had the highest BrØnsted acidity and total acidity and the added HSiW stabilizes the
tetragonal phase of zirconia. The catalytic activity was found to depend mainly on the HSiW
coverage. A bifunctional catalyst with alumina as the support was produced by Liu and co-workers
in 2015. They showed that increasing the calcination temperature from 350 to 650oC can lead to
structural evolution of the supported HSiW and a subsequent activity change. The Keggin structure
of HSiW began to dissociate around 450oC, causing the formation of various WOx species [171,
180]. TiO2 nanoparticles stabilized HPW in SBA-15 was prepared and calcined at different
temperatures (650–1000oC) it was found that the catalytic activity is mainly related with the
textural parameters and the acidity of the catalyst depends on the HPW coverage on the surface of
the catalyst and the calcination temperature. The calcination temperature 850oC was found to be
the best which is mainly due to the availability of the highest Brønsted acidity together with the
perfect monolayer coverage of HPW on the surface of the catalytic support [181a]. However, the
detailed structure evolution and the consequent activity changes with thermal treatment at elevated
temperature are still not clearly unveiled. Therefore thermal stability is one of the factors that is
considered in the design of heterogeneous HPAs based catalysts.
In this section, the effect of the calcination temperature of the 10Ni/30HSiW supported alumina
on the physico-chemical properties of catalysts and performance of the catalysts will be
investigated to optimize the catalytic properties and performance.
Experimental condition
The catalysts were prepared via the impregnation method. The obtained catalyst was heated in
flowing air to a particular temperature (350, 450, 550, and 650°C at 5°C/min), calcined for 5 h,
and then cooled to room temperature. Prior to each experiment, the catalyst was reduced in a quartz
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tubular reactor at 350oC. The effects of the calcined temperature on catalytic performance was
performed in a 300ml Hastelloy Parr batch autoclave using 30g glycerol, 70g DI water, 580PSI
Hydrogen at 240oC and 2g catalysts. The main products observed in the liquid phase were: acetol,
1,2-PD, 1,3-PD, acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products (OP) such
as methanol (MeOH), ethanol (EtOH) were also obtained. The properties of the prepared catalysts
were characterized using TPD, TPR, XRD and FTIR techniques.
Result and discussion
The performance of the catalyst calcined at different temperature is shown in Table 6-3 and Fig.
6-7. The main products observed in the liquid phase were: acetol, 1,2-PD, 1,3-PD, Acr, 1-PO and
EG. Some other products (OP) such as methanol (MeOH), ethanol (EtOH) were also obtained.
Table 6-3 Effect of calcination temperature on the conversion of glycerol and the distribution to
products in the hydrogenolysis of Glycerol
T, oC Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP
350 86.5 0.0 0.0 0.4 0.0 91.7 2.9 5.0
450 90.1 0.0 0.0 0.3 0.0 92.9 2.6 4.2
550 46.2 0.0 2.9 1.7 0.0 71.5 2.9 21.0
650 21.3 0.0 0.0 4.4 0.0 64.9 7.6 23.1
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. OP: By-products included methanol and ethanol.
130
Figure 6-7 Effect of calcination temperature on the conversion of glycerol and the distribution to
products as a function of time; A) Glycerol Conversion; B,C,D,E,F) Selectivity of acetol, 1,2-PD,
1-PO, Acr., other products, respectively. Reaction condition: 10Ni/30HSiW/Al2O3 catalyst,
240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and 580PSI of H2.
It is evident that the calcined temperature above 450oC affects both the conversion of glycerol and
product distribution significantly. Increasing the temperature of calcination, the conversion of
glycerol and selectivity went through a maximum of 90.1% and 92.9% respectively at a
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temperature of 450oC. The catalyst calcined at a temperature 450oC was found to produce the best
resultswith respect to 1-PO selectivity (92.9%) at high conversion (90.1%). The catalyst activity
is not affected by the calcination temperature below 450oC; there is only a slight difference in the
conversion of glycerol and product distribution and it is shown that the catalyst that was calcined
at 450oC had the optimal catalytic properties with respect to the conversion of glycerol and the
selectivity to 1-PO (90.1% and 92.9% respectively). On increasing of calcination temperature to
550oC, the conversion of glycerol and the selectivity to 1-PO decreased remarkably to 46.2% and
71.5% respectively; however the selectivity to acetol, acrolein and byproducts (mainly ethanol)
increase. The by-products significantly increased from 4.2% (450oC) to 21% (550oC). The
conversion of glycerol and selectivity to 1-PO decrease continuously to 23.1% and 64.9%
respectively with a further increasein the calcination temperature to 650oC. It is noticed that a
further increase of calcination temperature to 650oC does not show an increase in by-products but
results in an increase in the selectivity of acetol and acrolein (acetol increased from 1.7% (550oC)
to 4.8% (650oC) and acrolein increased from 2.9 to 7.6%). The catalytic performance of the
catalyst calcined at a higher temperature of 550oC and 650oC was depressed to a certain degree
compared to the catalyst calcined at 350 and 450oC.
Characterization
The acidic properties of the catalysts were probed using NH3-TPD. For a detailed analysis, the
TPD curves were deconvolved into 3 peaks (namely weak, medium and strong acid sites) using a
Gaussian fitting method, NH3-TPD profiles of the catalysts are shown in Fig. 6-8, and analysis of
the data is presented in Table 6-4.
It is seen that the calcination temperature plays an important role in controlling acid properties of
the catalysts. From the overall TPD curve areas, it was found that the total amount of acid sites
deacreased monotonously with increasing calcination temperature. However the decrease in total
acidity does not accompany the activity of the catalyst in term of glycerol conversion.
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Figure 6-8 NH3-TPD patterns for catalyst calcined at different temperature
Table 6-4 Effect of calcination temparature on acidity of 10Ni/30HSiW/Al2O3 catalyst
Increasing the temperature of calcination the conversion of glycerol and selectivity went through
a maximum of 90.1 and 92.9% respectively at 450oC. The catalyst calcined at a temperature of
450oC was found to produce the best results for 1-PO selectivity (92.9%) at high conversion
(90.1%). The reason for the high selectivity maybe due to the decrease in the acidity of the catalyst
making it less selective towards coke and the catalyst had a proper balance between dehydration
functions (acid sites) and hydrogenation (metal surface atoms). The classification of acid site
strength is indicated by the NH3-TPD; weak sites corresponding to 180–230oC, medium sites 390–
400oC and strong sites 430–470oC. The deconvoluted results showed two distinct trends as shown
Calc. Temp
oC
Weak acid site
mmol/g /(Temp.)
Medium acid site
mmol/g /(Temp.)
Strong acid site
mmol/g /(Temp.)
Total acid
amount, mmol/g
350 0.365/(196oC) 0.559/(389oC) 0.383/(432oC) 1.306
450 0.080/(207oC) 0.126/(396oC) 0.232/(433oC) 0.438
550 0.014/(185oC) - 0.051/(439oC) 0.065
650 0.011/(227oC) - 0.038/(470oC) 0.049
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in Table 6-4. First, the total number of acid sites decreased significantly as the calcination
temperature was increased. In particular, a large decline in acid site number was observed after
calcination at 550°C. The second trend was that apparently stronger acid sites were present as the
calcination temperature increased, the desorption maxima for NH3 were 432, 433, 439 and 470°C
after calcination at 350, 450, 550 and 650°C, respectively. When the catalyst was calcined at
temperatures below 450oC, 3 distinguished acid sites were observed and the intensity decreases
with the increasing calcination temperature. Further increasesin calcination temperature results in
a significant decrease in intensity of the acid sites in particular the medium acid sites that became
almost undetectable. The NH3-TPD experiments provide a good correlation between the adsorbed
amount of ammonia and the temperature of calcination: the higher the calcination temperature, the
lower is the amount of desorbing ammonia. Hence it could be concluded, that the proton as it is
suggested for the acidity of the catalyst are sufficient for chemically adsorbtion of ammonia and
that increasing the temperature reduces the amount of protosn of the catalyst which are responsible
for bonding ammonia. The relevance of the proton is emphasized by the effect of the calcination
temperature. The samples calcined at 650°C adsorb a lower amount of ammonia than those
calcined at 350°C which can be attributed to the loss of hydroxyl groups during calcination. The
reason for this loss is conceivable: dehydration at the surface.
Variations of the TPR profiles of the catalysts as a function of calcination temperature can be
helpful to interpret how components interact. The TPR profiles for the catalysts are shown in Fig.
6-9. As can be seen the TPR profiles of catalysts calcinated at 350 and 450oC are similar and as a
combination of two species of Ni and HSiW. However the TPR of the catalysts calcinated at higher
temperatures of 550 and 650oC were different from these two. It is suggested that the modification
in the structure of the catalyst occurred.
134
Figure 6-9 TPR patterns for catalyst calcined at different temperature
The catalysts were characterized with XRD to explore the crystal phases and to check possible
calcination temperature giving rise to distortion of the Keggin structure of the catalysts. The XRD
pattern of alumina support, bulk HSiW and the catalysts was showed in the Fig. 6-10.
Figure 6-10 XRD signal for catalyst calcined at different temperature
In Fig. 6-10, the same diffraction peaks of Al2O3 support are observed in all catalysts, well
corresponding to diffraction peaks of standard cubic Al2O3 [JCPDS No. 01-078- 2427]. XRD
135
patterns for the bulk HSiW showed distinct reflections (at 20o~24o, 26o~28o, 32o~35o). The peak
of HSiW could also be observed on the catalysts calcinated at 350 and 450oC, indicating the
presence of crystalline HSiW that proves that the Keggin structure is retained on the catalyst.
However, the diffraction peak of HSiW diminished and clear diffraction peaks assigned to
orthorhombic WO3 (654048-ICSD) nanocrystals were observed when the calcination temperature
was increased to 550 and 650 ◦C and the intensity of the diffraction peaks of orthorhombic the
WO3 phase increased with increasing calcination temperature. The result demonstrates that
tungstosilicic acid in the catalyst is, at least partially, dissociated into tungsten trioxide species
after treatment at 550 and 650◦C. It is consistent with the results Liu L. [171] observed on a
HSiW/Al2O3 catalyst.
FTIR spectra were employed to characterize the supported HSiW catalysts to investigate the
Keggin structure of the catalysts under thermal treatment. This technique can be used to confirm
the presence of the Keggin structure of HSiW on the support surface. Keggin anion at 978, 915,
885 and 798 cm−1 could be assigned to the typical antisymmetric stretching vibrations of W-O,
Si–O, W–O–W and W–O–W respectively [145]. The FTIR spectra of the catalysts are shown in
Fig. 6-11.
Figure 6-11 FTIR signal for catalyst calcined at different temperature
136
As can be seen, bulk HSiW has distinct absorption peaks at 978, 915, 885 and 798 cm−1, which
could be assigned to the typical antisymmetric stretching vibrations of W-O, Si–O, W–Oc–W and
W–Oe–W, respectively and the positions are in good agreement with those reported earlier,
[145,181b, 182]. It can be seen from the Fig. 6-11 that there was almost no change in the positions
of the characteristic bands for samples up to 450oC, confirming that the Keggin anion was
preserved in the catalyst up to this temperature . These peaks that present the Keggin structure of
HSiW also present on the catalyst calcined at 350 and 450oC but with relatively low intensity and
decreasing with increasing calcination temperature. This implies the presence of the Keggin ion in
the two catalysts, is well consistent with theTPD, XRD and TPR results. However, the first changes
in spectrum were registered at 550oc, which indicate the appearance of some new species in the
catalyst structure. It is evident that at high temperature, the Keggin anion had decomposed to SiO44-
(bands at about 1000cm-1) and WO42- ions (bands at about 860, 700 and 525cm-1). After
calcinations, the broad absorption peaks in the range 750–900cm-1 are characteristic of the
different O-W-O stretching vibrations in the WO3 crystal lattice [183-185]. On the other hand, the
observed broad peak at a wave number of 835cm-1 is assigned to the symmetric stretching
vibrations band of Si-O-Si, implying the formation of SiO2 [186]. Based on this analysis,
dissociation of the Keggin structure of HSiW is evidenced to occur at a calcination temperature of
550◦C and above
Summary
The total amount of acid sites deacreased monotonously with an increase in calcination
temperature. However the decrease in total acidity does not accompany the activity of the catalyst
in term of glycerol conversion. Increasing the temperature of calcination, the conversion of
glycerol and selectivity went through a maximum of 90.1 and 92.9% respectively at 450oC. The
catalyst calcined at a temperature of 450oC was found to produce the best results for 1-PO
selectivity (92.9%) at high conversion (90.1%). The reason for the high selectivity maybe due to
the decrease in the acidity of the catalyst making it less selective towards coke and the catalyst had
a proper balance between dehydration functions (acid sites) and hydrogenation (metal surface
atoms). To achieve good performance, catalysts must retain Keggin species on the surface, but
they must also have a proper balance between acid sites and metal sites. The supported
silicotungstic acid (HSiW) calcinated at 350 and 450◦C retained their crystal structure of Keggin
137
units; the decomposition and the degradation in the crystal structure of the catalyst may occur but
to a small extent. However increasing the calcination temperature to 550 and 650oC causes clear
decomposition of the Keggin structure.
6.2.2 The effect of reduced temperature
Reduction is also a crucial step in the catalyst preparation process. The reduction temperature can
influence the catalyst reducibility, thereby influencing the catalytic performance [187,188]. This
section deals with the effects of reduction temperature on the catalytic performance of
10Ni/30HSiW/Al2O3 catalysts for the hydrogenolysis of glycerol. The aim is to get some insight
into the relations between the catalyst preparation conditions (here catalyst reduction temperature)
and the catalytic properties of the studied catalysts (here catalyst activity and acidity). A set of 4
experiments were carried out under H2 media and the effect of reduction temperature (300oC,
350oC, 450oC and unreduced catalyst) on the catalytic performance was studied.
Experimental condition
The catalysts were prepared via the impregnation method. The obtained catalyst was calcinated in
flowing air at 350 for 5 h, and then cooled to room temperature. Prior to each experiment, the
catalyst was reduced in a quartz tubular reactor at different temperatures (300oC, 350oC, 450oC
and unreduced catalyst). The effects of the reduction temperature on catalytic performance was
performed in a 300ml Hastelloy Parr batch autoclave using 30g glycerol, 70g DI water, 580PSI
Hydrogen at 240oC and 2g catalysts. The main products observed in the liquid phase were: acetol,
1,2-PD, 1,3-PD, acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products (OP) such
as methanol (MeOH), ethanol (EtOH) were also obtained. The acidity of the prepared catalysts
were characterized using a TPD technique.
Result and discussion
The performance of the catalyst reduced at different temperature is shown in Table 6-5 and Fig. 6-
12.
138
Table 6-5 Effect of reduction temperature on the conversion of glycerol and the distribution to
products in the hydrogenolysis of Glycerol
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. OP: By-products included methanol and ethanol and
*: light and heavy, **: light
From the results summarized in Table 6-5, it is evident that the reduction is a crucial step in catalyst
treatment to obtain high selectivity to 1-PO and reduce the production of the by-products. Without
reducing, the selectivity to 1-PO was low at 67.5% but the selectivity to acrolein was high at 26.2%
at 71.3% glycerol conversion. Once the catalyst was reduced at 300oC the selectivity to 1-PO
significantly increased to 92.7% followed by a decrease of acrolein from 26.2% to only 2.4% at
76.3 conversion of glycerol. It is shown that a reduction temperature below 350oC affects slightly
the catalyst activity in term of conversion of glycerol and product distribution and the catalyst that
was reduced at 350oC had optimal catalytic properties for the formation of 1-PO (the yield of 1-
PO was 73.5%). With a further increase in the reduction temperature to 450oC the catalyst activity
in term of glycerol conversion remarkably decreases; the conversion of glycerol was only 43.8%.
The selectivity to 1-PO was also affected by the reduction temperature but it only as much as the
conversion of glycerol. Obviously, increasing the reduction temperature causes an inhibition effect
on the catalytic activity and selectivity to 1-PO, but it seems to be beneficial to promote the 1,2‐
PDO selectivity. To be specific, as the reduction temperature was raised from 350 °C to 450 °C,
the conversion of glycerol decreased from 81.1% to 43.8%, and the selectivity to 1-PO decreases
from 90.6 to 80.9% while the 1,2‐PD and acrolein selectivity increased from 0% to 2.9% and
Reduced
Temp.
Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr. OP
No 71.3 0.0 0.0 1.1 0.0 66.5 26.2 6.2*
300oC 76.3 0.0 0.8 0.5 0.0 92.7 2.4 3.6**
350oC 81.1 0.0 0.0 0.6 0.0 90.6 3.7 5.1**
400oC 64.3 0.0 0.9 0.8 0.0 89.7 5.0 3.7**
450oC 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.5
139
3.7% to 5.4% respectively. The decrease in activity of catalyst at high reduction temperature may
be caused by partial thermal decomposition that leads to a loss in protons. Hence the acidity of the
catalyst decreases and the catalyst becomes less effective for the dehydration step. As a result the
conversion of glycerol decreases and the further hydrogenolyis of 1,2-PD was slowed down.
Figure 6-12 Effect of reduction temperature on the conversion of glycerol and the distribution to
products as a function of time; A) Glycerol Conversion; B,C,D) Selectivity of acetol, 1-PO, Acr.,
other products, respectively. F) A comparison in rate constant k. Reaction condition:
10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI
water, 70g of DI water and 580 PSI of H2.
140
It is worth noting that the unreduced catalyst exhibited even higher activity than that of the catalysts
reduced at 400°C and 450°C. Although the activity of unreduced catalyst is similar to the activity
of catalysts reduced below 350oC in terms of glycerol conversion but there was a remarkable
difference in product distribution. The conversion of glycerol can reach 71%; however, the
selectivity to 1-PO was only 67.6% whilst the selectivity to acrolein was high. The glycerol
conversion and product selectivity as a function of time are shown in Figure 6-12. It can be seen
from Figure 6-12 that the selectivity to 1-PO (C) is increased but the selectivity to acrolein (D)
decreased. Using reduced catalyst, the selectivity to 1-PO and acrolein likely reached a stable state
and hardly changed after 2 hours of reaction. On the contrary, the selectivity to 1-PO increases
monotonously, while the selectivity to acrolein decreases gradually with increasing time when an
unreduced catalyst is used. One reasonable explanation for this trend is that under H2 media the
unreduced catalyst can be reduced in situ during the glycerol hydrogenolysis reaction so it can
promote the hydrogenation of acrolein as an intermediate to 1-PO leading to the selectivity to a 1-
PO increase but the selectivity to acrolein decreased with increasing time. This may be indicating
that the reduced catalyst can influence the catalytic performance by promoting active hydrogen
species on the metal sites and generate in the active sites of the catalyst.
Figure 6-13 Pseudo-first-order kinetic plots for 10Ni/30HSiW/Al2O3 Catalyst reduced at different
temperature. Reaction condition: 240ºC, 580PSI of H2, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water.
141
Characterization
To examine surface acidity, NH3-TPD was performed and the results are shown in Table 6-6 and
Fig. 6-14. For a detailed analysis, the TPD curves were deconvolved, using a Gaussian curve fit of
three bands as shown in Table 6-6. Thus the low temperature peak at around 190oC is attributed to
weak acid sites, 330oC is attributed to medium acid sites and the peak at around 440oc is
attributable to strong acid sites. From the overall TPD curve areas, it can be seen that on increasing
the reduction temperature the acidity of the catalyst went through a maximum of 0.911 mmol/g at
a 400oC reduction temperature. First, the total number of acid sites increased monotonously as the
reduction temperature increased from 300 to 400oC. A further increase in the reduction
temperature leads to a decrease in the total number of acid sites. The increase in the amount of
acidity was also accompanied by the change in the strength of the acidity. It can be seen that there
is a similar change in strong acid sites with increasing reduction temperature. First, the strength of
the acidity also increased as the reduction temperature was increased from 300 to 400oC (shift of
strong acid sites from 419oC to 443oC). A further increase in the reduction temperature leads toa
decrease in the strength of the acidity (shift of strong acid sites to 436oC).
Figure 6-14 NH3-TPD patterns for catalyst reduced at different temperature
142
Table 6-6 Effect of reduced temparature on acidity of 10Ni/30HSiW/Al2O3 catalyst
However an increase in total acidity does not absolutely accompany the activity of the catalyst in
terms of glycerol conversion. The catalyst that was reduced at 350oC had the optimal catalytic
properties with respect to the conversion of glycerol and the selectivity to 1-PO. The reaction rate
is the highest when the catalyst was reduced at 350oC (Fig. 6-13).
Summary
In summary, it is crucial to reduce the catalyst to obtain high selectivity of 1-PO. The selectivity
to 1-PO decreased with increasing catalyst reduction temperature above 400oC indicating that the
catalyst activity may be weakened at high reduction temperature. However over the range of 300
to 450oC of reduction temperature, the change in acidity of the catalyst was not accompanied by a
change in the activity of the catalyst. Although the catalyst reduced at 300oC has the lowest acidity
it can possess an activity similar to the catalyst reduced at 350oC that has much higher acidity. The
catalyst reduced at 450oC has the highest acidity but its activity was much lower than the catalysts
reduced at 300 and 350oC. The reason for the low activity maybe due to the increase in acidity of
catalyst making it more selective towards coke formation [189]. The catalyst that has low acidity
but high activity, is a result of a proper balance between dehydration functions (acid sites) and
hydrogenation (metal surface atoms). To achieve good performance, catalysts must have a proper
balance between acid sites and metal sites
Reduced
Temp.
Weak acid site,
mmol/g /(Temp.)
Medium acid site
mmol/g /(Temp.)
Strong acid site
mmol/g /(Temp.)
Total acid amount,
mmol/g
300oC 0.146/ (187oC) 0.270/ (346oC) 0.151/ (419oC) 0.568
350oC 0.180/ (182oC) 0.504/ (335oC) 0.196/ (441oC) 0.880
400oC 0.208/ (179oC) 0.460/ (319oC) 0.242/ (443oC) 0.911
450oC 0.230/ (189oC) 0.396/ (335oC) 0.170/ (436oC) 0.796
143
6.3 Effect of different supports on activity of 10Ni/30HSiW supported catalyst
It is well-known that the disadvantage of HPAs relates to low thermal stability, low surface area
(<10 m2/g) and leaching problems of the species into reaction mixture which limit the application
of HPA catalysts in current industry to some extent. Amongst the main factors determining activity
and the stability of such catalysts is the nature of the supports. Therefore to overcome these
disadvantages and make the catalyst more feasible, proper supports should be employed to disperse
the active phase. The choice of a support is generally guided by the increased specific surface area,
which leads to a high number of accessible active sites. However the development of HPA catalysts
possessing higher thermal stability is an important challenge. [190,191]. Besides, the acidity and
catalytic activity of the supported HPAs also depend mainly on the type of carrier and on the
loading. The increased thermal stability is ascribed to the aforementioned interaction between the
support and the heteropoly anion. If the interaction with the support is strong, the acidic strength
of the HPA may reduce due to the distortion of its structure leading to the activity of the final
catalyst being much lower than that of the HPAs itself, but this interaction also stabilizes the
Keggin structure and hinders its thermal decomposition; whereas low interactions of HPAs with
the supports could lead to dramatic leaching. This effect has been described by Alta et al for
alumina supported heteropoly acids [76].
It is of high interest to obtain a deeper insight of the influence of the support character on the
catalytic behavior of Ni/HSiW catalysts. In order to be able to clearly present many aspects
concerning the 10Ni/30HSiW catalysts, it was decided to investigate the influence of different
supports on the catalytic behavior of 10Ni/30HSiW catalysts. The aim of this work was to study
the acidity and catalytic activity of different supports.
Atia et al. [192] claimed that alumina-supported HPA showed higher catalytic activity and acrolein
selectivity than silica-supported acid, although the reported selectivity did not exceed that of what
Tsukuda [170].
It has been reported that MCM41 that has higher surface area, a regular pore size arrangement and
is a thermally stable material (T>1000), which can be a promising candidate as a supporting
material in doping of heteropolyacids for catalytic applications in acidic regions. Good dispersion
of the active component over the whole surface enhances the yield of the processes by increasing
144
the accessibility to active sites [193-196]. Titania, is a widely used catalyst support [197], and is
known to enhance the activity in many cases due to the strong interaction between the active phase
and the support [198]. It is reported that TiO2-supported HPAs are more active and resistant and
preserves the Keggin unit at a higher temperature than the corresponding bulk HPAs. [199, 200].
The crystalline structure and thermal stability of HSiW are not compromised after deposition on
TiO2 and the Keggin structure is preserved at temperatures up to 450oC [201]
In this section, several supports for 10Ni/30HSiW catalyst were prepared, characterized, and tested
in aqueous solution for glycerol hydrogenolysis. The aim of the present investigation was to
compare the catalytic activity of catalysts containing HSiW, one of the strongest heteropolyacids,
supported on alumina with the activity of the catalysts containing the same heteropolyacids
supported on commonly used oxides: Titania and MCM-41.
Experimental condition
The effects of the different support on catalytic performance was performed in a 300ml Hastelloy
Parr batch autoclave using 30g glycerol, 70g DI water, 580PSI Hydrogen at 240oC and 2g catalysts.
The catalysts were prepared via the impregnation method. Prior to each experiment, the catalyst
was reduced in a quartz tubular reactor for 5 hours. The main products observed in the liquid phase
were: acetol, 1,2-PD, 1,3-PD, acrolein (Acr), 1-PO and ethylene glycol (EG). Some other products
(OP) such as methanol (MeOH), ethanol (EtOH) were also obtained. The properties of the prepared
catalysts were characterized using TPD, XRD techniques.
Result and discussion
Effect of the support on the catalytic activity of 10Ni30HSiW catalysts in the hydrogenolysis of
glycerol to other chemicals was examined at 2 different reduction temperatures of 350oC and
450oC. The results after reaction for 7 h are shown in Table 6-7.
As can be observed, the activity of MCM-41 and TiO2 supported catalysts seems to be not affected
by high treatment temperature of 450oC; however, the catalyst supported alumina does. The
activity of the different supported catalyst was in the order of Al2O3<TiO2<MCM-41. In all cases,
1-PO is produced as the main product. Among the catalysts, the catalyst supported MCM-41
appears to be the most active for the production of 1-PO from glycerol and its activity is apparently
145
not affected by the reduction temperature. The conversion of glycerol and the product distribution
are similar for both catalysts reduced at 350 and 450oC that the selectivity to 1-PO can reach around
90% at 87% glycerol conversion.
Table 6-7 Effect of support on the conversion of glycerol and the distribution to products in the
hydrogenolysis of Glycerol
Reaction condition: 10Ni/30HSiW/Al2O3 catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol
(30wt%), 70g of DI water and 580PSI of H2. *OP: By-products included methanol and ethanol;
**OP: By-products included methanol and ethanol;
Support Red.
temp
Conv.
mol%
Selectivity, mol%
1,3-PD 1,2-PD Acetol EG 1-PO Acr OP
Al2O3 350 72.3 0.0 1.1 0.6 0.0 91.7 3.1 3.5*
450 43.8 0.0 2.9 1.2 0.0 80.9 5.4 9.6*
TiO2 350 68.5 0.0 1.4 0.5 0.0 91.5 2.7 3.9*
450 81.7 0.0 0.5 0.6 0.0 88.9 6.6 3.5*
MCM-41 350 87.7 0.0 0.3 0.6 0.0 89.2 4.3 5.6**
450 87.8 0.0 0.9 0.3 0.0 90.9 2.7 5.2*
146
Figure 6-15 Effect of supports reduced at 350oC on the conversion of glycerol and the
distribution to products as a function of time; A) Glycerol Conversion; B,C,D,E,F) Selectivity of
acetol, 1,2-PD, Acr., 1-PO, other products, respectively. Reaction condition: 10Ni/30HSiW
supported catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and
580PSI of H2
147
Figure 6-16 1Effect of supports reduced at 450oC on the conversion of glycerol and the
distribution to products as a function of time; A) Glycerol Conversion; B,C,D,E,F) Selectivity of
acetol, 1,2-PD, Acr., 1-PO, other products, respectively. Reaction condition: 10Ni/30HSiW
supported catalyst, 240ºC, 700RPM, 2g catalyst, 30g of glycerol (30wt%), 70g of DI water and
580PSI of H2
Figure 6-17 Effect of supports on Glycerol Hydrogenolysis and products selectivity: A) Catalyst
reduced at 350oC; B) Catalyst reduced at 450oC. Reaction condition: 240ºC, 700RPM, 2g catalyst,
30g of glycerol (30wt%), 70g of DI water and 580PSI of H2.
148
Figure 6-18 Pseudo-First-Order kinetic analysis of effect of support on hydrogenolysis of glycerol
in the presence of 10Ni/30HSiW/Al2O3 catalyst; Reaction condition: 240ºC, 700RPM, 2g
catalyst, 30wt% aqueous glycerol and 580PSI H2
The high reduction temperature affects slightly the activity of the catalyst supported TiO2 in terms
of glycerol conversion to some extent but it does not affect the product distribution. The selectivity
to 1-PO can reach around 89.2% at the 81.7% glycerol conversion. Although at a low treatment
temperature of 350oC, the activity of alumina supported catalyst can compete with the activity of
Titania supported catalyst with respect to both glycerol conversion and the product distribution;
however, the reduction temperature at 450oC affects strongly the activity of alumina supported
catalyst. Increasing of treatment temperature to 450oC decreases the activity of alumina supported
catalyst significantly. The conversion of glycerol significantly decreases from 72.3% to only
43.8% and the selectivity drops from 91.7% to only 80.9%.
Charaterization
The NH3-TPD was performed from 50 to 750◦C to study the acidic properties on the catalyst
surface conducted in order to elucidate the catalytic activity of catalysts, and thus, to find out how
a support can affect the catalytic activity and acid property of the 10Ni/30HSiW supported
catalysts. The NH3-TPD profiles of different support catalysts reduced at 450oC were deconvoluted
into 3 peaks (namely weak, medium and strong acid sites) using a Gaussian fitting method and are
shown in Fig. 6-19. The total acidity of the catalysts was recorded and is shown in Table 6-8 and
149
was then correlated with the catalytic activity of 10Ni/30HSiW supported catalysts (Fig. 6-18 and
Fig. 6-19). Roughly, different kinds of support represented a difference in the total acidity amount,
the strength of acid sites and a positive correlation is observed between activity of the catalyst and
acid amount over different supported catalysts.
Figure 6-19 NH3-TPD patterns for different support.
Table 6-8 Surface area and acidities of 10Ni/30HSiW supported catalysts
As can be seen, the MCM-41 supported catalyst shows the highest acidity while the alumina
supported catalyst gives a low acidity among all catalysts (Fig. 6-20). The total acidity is in the
order of MCM-41>TiO2>Al2O3, a similar trend was also observed for the strength of medium acid
sites. These results suggest that the acidity of HSiW is affected by the support. It is noticeable that
the trend of catalytic activity is well consistent with the trend of the amount of acidity of these
catalysts; the most active catalyst is the one that possesses the highest acidity and the strength of
Support
SAA
m2/g
Weak acid site
mmol/g
/(Temp.)
Medium acid
site, mmol/g
/(Temp.)
Strong acid
site, mmol/g
/(Temp.)
Total acid
amount, mmol/g
Acidity/SAA
mmol/m2
Al2O3 21.2 0.232/ (189oC) 0.396/ (335oC) 0.168/ (436oC) 0.796 0.038
TiO2 18.1 0.219/ (191oC) 0.462/ (342oC) 0.153/(449oC) 0.834 0.046
MCM-41 560.5 0.354/ (176oC) 0.702/ (355oC) 0.483/ (446oC) 1.539 0.0027
150
medium acid sites (Table 6-7 and Fig. 6-20). The higher the acidity the higher the conversion of
glycerol and selectivity to 1-PO (Fig. 6-21)
Figure 6-20 Effect of supports on total acidity and acid strength of catalyst reduced at 450oC
Figure 6-21 Effect of acidity of catalyst on glycerol conversion and selectivity of products
The catalysts were characterized with XRD to explore the crystal phases and to check possible if
the interactions between the support and HSiW can affect and distort the structure of the HSiW
151
supported catalysts. Fig. 6-22 shows the X-ray diffraction patterns of alumina support, bulk HSiW
and 10Ni/30HSiW supported catalysts
Figure 6-22 XRD patterns for different support
As shown in Fig. 6-20, all supported catalysts show that the diffraction peaks corresponded to the
support itself that is refered to the JCPDS database. Anatase TiO2 (centered at 2θ = 25.4, 38.0,
and 48.2, 54, 55, 63, 69, 71) are in good agreement with the standard spectrum (JCPDS no.: 84-
1286) [202]. Alpha alumina (centered at 2θ= 25.6, 35.2, 37.8, 43.4, 52.6, 57.5 and 61.3) are in
good agreement with the standard spectrum (JCPDS no.: 42-1468)[203]. Wide angle X-ray
diffraction patterns of MCM-41ares in good agreement with that of Jha A. et al. reported in his
work, a broad band in the range of 2θ = 15−40°, which is a characteristic of siliceous material
[195]. Besides the diffraction peaks that attributed to HSiW are observed for all catalysts confirms
that the Keggin structure is preserved upon the impregnation of the HSiW onto different supports
under the catalytic system.
BET surface area was calculated from desorption isotherms and the result are listed in Table 6-8.
As can be seen from Table 6-8, amongst the supports, the MCM-support catalysts have the largest
surface area.Thist may contribute to more acid sites that this catalyst possesses and as a result the
152
increase in glycerol conversion is believed to be higher when the amount of acid sites produced is
higher by introducing more surface area.
Summary
The support clearly affects the catalyst activity. Among the supports, the catalyst supported MCM-
41 possesses the highest acidity and catalyst activity. This support can retain the activity of catalyst
at high reduction of 450oC. This was also observed for the catalyst supported TiO2 but the catalyst
activity is a bit lower compared to that of MCM-41. At low temperature treatment, an alumina
support can compete with TiO2; however the catalyst loses its activity quickly at high temperature.
MCM-41 and TiO2 can be a good support for the hydrogenlysis of glycerol to 1-PO using a
10Ni/30HSiW supported catalyst.
6.4 Conclusion
In this chapter, catalysts have been tested and characterized using different catalyst
characterization techniques to study the relationship between the catalyst structure and the catalytic
activity.
It is found that the structure of catalyst can be affected in the activation process such as calcination
or reduction. The loss in activity of catalyst may occur if the treatment temperature is higher than
450oC. Under our catalytic system, the HSiW supported catalyst calcined at 450oC and reduced
at 350oC is the best candidate for 1-PO production and the catalyst needs to be reduced to obtain
high selectivity of 1-PO. The decomposition of HPMo already occurred at 350oC treatment and
HPMo supported catalyst is inactive in this reaction.
To achieve good performance, catalysts must retain the Keggin species on the surface which is
probably beneficial to induce BrØnsted acid site that can cleave the secondary – OH group in
glycerol; they must also have a proper balance between acid sites and metal sites. The crystal
structure of the Keggin unit of the HSiW supported catalyst is decomposed at least partially when
the calcination temperature increased to 550◦C. The support clearly affects the catalyst activity.
Among the supports, the catalyst supported MCM-41 possesses the highest acidity and catalyst
actitvity. MCM-41 and TiO2 can be a good supports for the hydrogenlysis of glycerol to 1-PO
using 10Ni/30HSiW supported catalyst.
153
Chapter Seven
Conclusion and Recommendation
7.1 Conclusions on glycerol hydrogenolysis to 1-PO using 10Ni/30HSiW supported catalyst
To my knowledge, this is the first time the one-pot hydrogenolysis of glycerol to 1-PO using non-
noble-metal of Ni-based supported HSiW/Al2O3 catalyst have been successfully carried out in
water with high selectivity to 1-PO (92%) at high conversion of glycerol (90%). Further
development could potentially lead to a new green process for the production of sustainable 1-PO.
The bifunctional catalyst of 10Ni/30HSiW/Al2O3 was successfully prepared in water through a
one step of impregnation (co-impregnation of Ni and HSiW) with high catalyst activity. This
served as a cheaper and efficient alternatives method compared to that was prepared by a
conventional sequential impregnation method.
Among the metals (Cu, Ni, Pd, and Pt) supported on 30HSiW/Al2O3, Pt is the best promoter for
the production of 1,3-PD from glycerol,however using. Ni, a much cheaper metal has fairly
comparable reactivity to Pt. Although it is reported that Cu possesses good hydrogenation activity
that is comparable with Ni, Cu does not show activity for the production of 1,3-PD under these
reaction conditions.
Cs+ has little effect on glycerol conversion; however it shows a significant effect on the product
distribution – due to reduction of acidity. The 10Ni/30HSiW/Al2O3 catalyst was found to be an
effective catalyst for the production of 1-PO, whereas, Cs+ exchanged catalyst becomes effective
for the production of 1,2-PD and EG. A greater quantity of acid sites of a medium strength
corresponded to a higher selectivity of 1-PO. XRD data shows that hydrogen protons in the
secondary structure may be replaced by Cs+ that corresponds to the decrease in the acidity of the
catalyst. Among the catalysts tested, 1Cs+ catalyst showed the best catalytic performance for 1,3-
PD and 1-PO; however, fully substituted NiCs4SiW12O40 is catalytically inert to 1-PO as it
possesses very low acid sites. Ni plays an important role for the production of lower alcohols due
to its hydrogenation activity. Without Ni, the substitution of H+ by Cs+ decreases the activity of
30HSiW/Al2O3 significantly.
154
It is found that the hydrogenlysis of glycerol is chemically controlled at a stirring speed of 500
RPM in a batch reactor. The conversion of glycerol is inversely proportional to the hydrogen
pressure. This possibly could be attributed to the fact that the reduction of W under high pressure
of H2 results in the loss of activity of the catalyst for the dehydration step that leads to a decrease
in the conversion of glycerol. However a high H2 pressure is necessary to suppress the undesired
dehydration and to decrease the undesired products. Optimal operating H2 pressures are required
to obtained high yields of 1-PO.
Dilute feed solutions favor the selectivity to 1-PO but decreases the conversions of glycerol.
Increasing the glycerol concentration (decreasing the initial water content) decreased the
selectivity to 1-PO while meanwhile the selectivity to 1,2-PD and acrolein increased. The increase
in the concentration of glycerol may result in less active sites becoming available for the
conversion of 1,2PD and/or acrolein to 1-PO, so more 1,2-PD and/or acrolein can be retained and
less 1-PO is produced. Optimal glycerol feed concentration is required to obtain a high yield of 1-
PO.
Conversion increased with catalyst loading, but selectivity had a maximum of 92.7% at 4.5%
loading. It is thought that high catalyst loadings tend to provide excess active sites resulting in
increased exposure of 1-PO to the surface of catalyst that can promote the further degradation of
1-PO or promote the side reactions from glycerol to produce undesired products causing a decrease
in 1-PO selectivity. Optimal catalyst loading is required to obtain a high yield of 1-PO.
Increasing temperature may promote further hydrogenolsis of 1,2-PD to 1-PO. However excessive
heat may cause the degradation of 1-PO to other products or promote other side reactions.
Therefore it is suggested that the operation at high hydrogen pressures may prevent degradation of
products.
According to acidity,1-PO was favored by catalyst acidity while 1,2-PD and EG are likely favored
by basicity and the loading of HSiW should be at least 20% to promote the futher hydrogenlolysis
of 1,2-PD to 1-PO. It is believed that part of 1-PO came from the hydrogenation of acrolein that
was produced from the consecutive dehydration of glycerol. The total number of acidic sites and
the acid strength was found to decrease with increasing Ni content. A decrease in acidity may
155
possibly be due to the covering of acid sites by Ni or it can be suggested that this behavior may
result from direct anchoring on proton sites and from blockage of acid channels by Ni particles.
It is found that the structure of catalyst can be affected in the activation process such as calcination
or reduction. The loss in activity of the catalyst may occur if the treatment temperature is higher
than 450oC. Under our catalytic system condition, the HSiW supported catalyst calcined at 450oC
and reduced at 350oC is the best candidate for 1-PO production and the catalyst needs to be reduced
to obtain high selectivity of 1-PO. The decomposition of HPMo already occurred at 350oC of
treatment and HPMo supported catalyst is inactive in this reaction.
To achieve good performance, catalysts must retain the Keggin species on the surface which is
probably beneficial to induce BrØnsted acid sites that can cleave the secondary – OH group in
glycerol; they must also have a proper balance between acid sites and metal sites. The crystal
structure of the Keggin unit of the HSiW supported catalyst decomposed at least partially when
the calcination temperature increased to 550◦C. A greater quantity of acid sites of a certain strength
corresponded to a higher selectivity of 1-PO.
The support clearly affects the catalyst activity. Among the supports, the catalyst supported MCM-
41 possesses the highest acidity and catalyst actitvity. Preliminary results indicated that MCM-41
and TiO2 are good supports for the hydrogenlysis of glycerol to 1-PO using a 10Ni/30HSiW
supported catalyst.
Although 10Ni/30HSiW supported catalyst shows a good acitivity for the production of 1-PO from
glycerol; the leaching of catalyst is a concern.
7.2 Proposed reaction pathway
Based on our experimental results, we propose the following reaction pathway to explain the
glycerol hydrogenolysis over a 10Ni/30HSiW supported catalyst (Scheme 7-1). The first
intermediate products for glycerol conversion are acetol and 3-hydroxypropionaldehyde (3-HPA)
which are formed via the dehydration of the hydroxyl group at the secondary and primary carbon
atom respectively. 1,2-PD is formed from the hydrogenation of acetol while hydrogenation of 3-
HPA produces 1,3-PD. In the absence of an efficient hydrogenation function on an acidic catalyst,
3-HPA will undergo dehydration to form acrolein. Further hydrogenolysis of 1,2-PD or 1,3-PD
156
gives 1-PO. Since 3-HPA is more reactive compared to acetol [59, 166], it was not observed as an
intermediate in the reaction. From the mechanism proposed, 1-PO could be obtained from the
hydrogenolysis of 1,2-PD and 1,3-PD, or the hydrogenation of acrolein.
Scheme 7-1 Reactions in the hydrogenolysis of glycerol to 1-PO using bifunctional catalyst of
10Ni/30HSiW/Al2O3
With acidic catalysts, the formation of 1,2-PD, 1,3-PD and 1-PO is proposed as in the scheme 7-
1. When H+ was substituted by Cs+ or at low HSiW loading proposed pathways for the conversion
of glycerol to glycols (1,2-PD and EG) are shown in Scheme 7-2.
Scheme 7-2 Proposed pathways in the hydrogenolysis of glycerol to 1,2-PD and EG using a
bifunctional catalyst with low acidity
When H+ was replaced by an alkaline metal ion, Cs+, the acidity of the catalyst decreases while
the basicity of the catalyst may increase. Hence it is possible that the formation of 1,2-PD and
EG takes place through a reversible dehydrogenation of glycerol to glyceraldehyde (GA) on metal
sites, followed by dehydration or retro-aldolization of GA on basic sites to 2-
157
hydroxyacrylaldehyde or 2-hydroxyacetaldehyde, and finally, the two aldehyde precursors are
hydrogenated on metal sites to 1,2-PD and EG, respectively.
7.3 Recommendations
The much lower price of Ni compared to Pt is very attractive for a new green process development
for the conversion of glycerol to sustainable higher value products. To obtain a desired product
selectively, the control of reaction conditions and catalyst properties such as acid strength, the
amount of appropriate acid sites and metal hydrogenation activity will be needed. Optimization
of the catalyst preparation techniques and a balance of Ni and HiSiW loading on various supports
could lead to high yields of value-added chemicals from glycerol. Due to the inexpensive Ni-based
catalyst and the high selectivity, an economical production of green and sustainable 1-PO from
glycerol hydrogenolysis may be feasible for future commercial development.
10Ni/30HSiW supported catalysts seem to be a good catalyst system for the production of 1-PO
from glycerol. MCM-41 or TiO2 can be a choice of support to make the catalyst work effectively.
It is suggested that that catalyst should be prepared by co-impregnation, since under this catalytic
system this catalyst can perform better compared to other catalyst preparation sequences. This
method also saves time and requires less work to prepare the catalyst. However, the direct
interaction between the components during the preparation should be considered.
The studied catalytic system is effective for the production of 1-PO from glycerol and it is known
that the dehydration of 1-PO will produce propene. Therefore it is promising to develop new routse
for one-step propylene production from glycerol based on this catalytic system.
It is found that the 10Ni/30HSiW/Al2O3 catalyst is effective for the hydrogenolyis of 1,2-PD to 1-
PO (at high conversion of glycerol of 98.1% and high selectivity to 1-PO of 91%) so the 2 layer
catalyst packing can also be developed for the production of 1-PO from glycerol.
However, it has been discussed that the catalyst leaching and deactivation in a glycerol
hydrogenolysis process is possible; therefore, the development of a catalyst supported
heteropolycaid needs to be studied to facilitate the improvement of catalytic performance and to
make it widely used.
158
It was found that when the hydrogenolysis of glycerol was performed in a Stanless steel reactor,
the reaction rate was much lower compared to when it was carried out in a Hastelloy reactor;
however, the selectivity to 1,3-PD was much higher. It is thought that the release of metal
constituent from stainless steel reactor into the solution may occur and affect the product
selectivity. This was also reported by Chaminand J. et. al. that partial dissolution of metals from
the inox walls of the reactor increased the selectivity to 1,3-PD in the hydrogenolysis of glycerol
on heterogeneous catalysts [56]. Therefore, a study of promoter effects, e.g. adding another metal
component such as Fe, for the activity of catalyst to form 1,3-PD may be of interest. To improve
the selectivity of 1,3-PD it is suggested that the catalyst should have high hydrogenation activity
for the intermediate 3-HPA. The equilibrium between acrolein and 3-HPA in the hydration-
dehydration step is important, so it is essential to tune the bi-functional catalyst and the conditions
of the reaction to form 1,3-PD from 3-HPA. A statistical analysis on the effect of catalyst
compositions, the conditions of the reaction on 1,3-PD selectivity from glycerol can be applied to
this study. The effect of catalyst composition can be studied through response surface
methodology (RSM) combined with a central composite rotatable design (CCRD). A DRIFT
technique can be applied for in-situ studying of the intermediate species for 1,3-PD on the catalyst.
Chemisorption studies and density functional density theory (DFT) modelling can be applied to
investigate the structures and interactions between the reactants and the catalyst surface to
elucidate a potential mechanistic pathway for the catalytic reactions.
159
References
1. Hatti-Kaul, R., Törnvall U., Gustafsson L., Börjesson P., Industrial biotechnology for
the production of bio-based chemicals-a cradle-tograve perspective. Trends Biotechnol,
2007, 25, 3, 119-124
2. Sheldon R.A., Why green chemistry and sustainability of resources are essential to our
future. J. Environ. Monit., 2008, 10, 4, 406-407
3. Okkerse C. and Bekkum H.V., From fossil to green. Green Chem., 1999, 1, 2, 107-114
4. James H.C., Fabien I. D., Introduction to chemical from biomass, John Wiley and Sons,
United Kingdom, 2008
5. Anastas. P. T., Warner. J. C., Green Chemistry: Theory and Practice, Oxford University
Press: New York, 1998
6. Bagheri S. et al., Catalytic conversion of biodiesel derived raw glycerol to value added
products, Renewable and Sustainable Energy Reviews, 2015, 41, 113–127
7. Ye X. P., Ren S., Value-Added Chemicals from Glycerol, ACS Symposium Series;
American Chemical Society: Washington, DC, 2014, Chapter 3, pp 43–80
8. Pagliaro M., Ciriminna R., Kimura H., Rossi M., Pina C.D., Recent advances in the
conversion of bioglycerol into value-added products, Eur. J. Lipid Sci. Technol., 2009,
111, 788–799
9. Bozell J. J., Petersen G. R., Technology development for the production of biobased
products from biorefinery carbohydrates—the US Department of Energy’s “Top 10”
revisited, Green Chem., 2010, 12, 539-554
10. Förare J., Swedish Research and Innovation Strategy for a Bio-based Economy, 2012,
ISBN:978-91-540-6068-2,
11. Christoph R., Schmidt B., Steinberner U., Dilla W,. Karinen R., "Glycerol", Ullmann's
Encyclopedia of Industrial Chemistry. Online Edn, 2006, Germany, Wiley-VCH,
Weinheim.
12. Patel M.K., Crank M., Dornburg V., Recchia E., Medium and long-term opportunities
and risks of the biotechnological production of bulk chemicals from renewable
resources- The potential of white biotechnology. The BREW Project, 2006
160
13. Dasari M.A., Kiatsimkul P.P., Sutterlin W.R., and Suppes G.J., Low-pressure
hydrogenolysis of glycerol to propylene glycol, Applied Catalysis A: General, 2005,
281, 1-2, 225-2311
14. Nilles D., Combating the glycerin glut. Biodiesel Magazine, 2006
15. Yang F. X., Hanna M. A., Sun R. C., Value-added uses for crude glycerol-a byproduct
of biodiesel production, Biotechnol. Biofuels, 2012, 5, 13
16. Johnson D. T., Taconi K. A., "The glycerin glut: Options for the value-added conversion
of crude glycerol resulting from biodiesel production," Environmental Progress, 2007,
26, 338-348
17. Pagliaro M., Ciriminna R., Kimura H., Rossi M., Pina C. D., "From glycerol to value-
added products." Angewandte Chemie - International Edition, 2007, 46, 24, 4434-4440
18. Werpy T., Peterson G., Aden A., Bozell J., Holladay J., White J., Manheim, A. Top
value added chemicals from biomass, Volume 1: Results of screening for potential
candidates from sugars and synthesis gas. United States Department of Energy
Efficiency and Renewable Energy, 2004
19. Jong, E.D., et al., Bio-based chemicals - value added products from biorefineries. IEA
Bioenergy, 2012
20. Jang, Y.-S., et al., Bio-based production of C2–C6 platform chemicals. Biotechnology
and Bioengineering, 2012, 109, 10, 2437-2459
21. Pagliaro M., Rossi M., The Future of Glycerol. Cambridge, The Royal Society of
Chemistry, 2010
22. Kenar J. A., "Glycerol as a platform chemical: Sweet opportunities on the horizon?"
Lipid Technology, 2007, 19, 249-253.
23. Dube M. A., Tremblay A. Y., Liu Y., "Biodiesel production using a membrane reactor."
Bioresource Technology, 2007, 98, 3, 639-647
24. Zhou C.H., Beltramini J.N., Fan Y.X. and Lu G.Q., Chemoselective catalytic
conversion of glycerol as a biorenewable source to valuable commodity chemicals,
Chemical Society Reviews, 2008, 37, 527–549
25. M. Pagliaro and M. Rossi, The Future of Glycerol: New Usages for a Versatile Raw
Material. Cambridge: RSC Publishing, 2008
161
26. Corma, S. Iborra, and A. Velty, "Chemical Routes for the Transformation of Biomass
into Chemicals," Chemical Reviews, 2007, 107, 2411-2502
27. Behr A., J. Eilting, K. Irawadi, J. Leschinski, and F. Lindner, "Improved utilisation of
renewable resources: New important derivatives of glycerol," Green Chemistry, 2007,
10, 13-30
28. a. https://www.zauba.com/shipment_search; b. Jiang W. et al., Key enzymes catalyzing
glycerol to 1,3-propanediol, Biotechnol Biofuels, 2016, 9, 57-75
29. Wang Y et al., Catalytic hydrogenolysis of glycerol to propanediols: a review, RSC
Adv., 2015, 5, 74611–74628
30. Saxena R.K., Anand P., Saran S., Jasmine I., Microbial production of 1,3-propanediol:
Recent developments and emerging opportunities, Biotechnology Advances, 2009, 27,
895-913
31. Product Safety Summary Sheet - DuPont Tate & Lyle BioProducts™ 1,3-Propanediol
32. Value-added Utilization of Crude Glycerol from biodiesel Production: A Survey of
Current Research Activities, An ASABE Meeting Presentation, Paper Number: 066223
33. Hellman T.M., Small F.H., Characterization of the odor properties of 101
petrochemicals using sensory methods. J. Air Pollut. Control Assoc., 1974, 24, 979-982
34. Jain R, Yan Y, Dehydratase mediated 1-propanol production in metabolically
engineered Escherichia coli. Microb Cell Fact 2011, 10,1–10
35. Shen C.R., Liao J.C., 2008. Metabolic engineering of Escherichiacoli for 1-butanol and
1-propanol production via the keto-acid pathways. Metab.Eng. 2008, 10, 312–320
36. "1-Propanol. http://www.inchem.org/documents/ehc/ehc/ehc102.htm
37. Material Safety Data Sheet 1-Propanol. Caledon Laboratory chemicals
[http://www.caledonlabs.com/upload/msds/8500-1e.pdf]
38. Product Safety Assessment: DOW™ 1-propanol, page 2; James L. Unmack, 1-propanol
Health-Base Assessment and Recommendation for HEAC
39. http://www.syntecbiofuel.com/propanol.php
40. Atsumi S, Liao JC, Directed evolution of Methanococcus jannaschii citramalate
synthase for biosynthesis of 1-propanol and 1-butanol by Escherichia coli, Appl
Environ Microbiol 2008, 74, 7802–7808
162
41. Atsumi S., Cann A.F., Connor M.R., Shen C.R., Smith K.M., Brynildsen M.P., Chou
K.J.Y., Hanai T., Liao J.C., Metabolic engineering of Escherichia coli for 1-butanol
production. Metab Eng 2008, 10, 305–311
42. Bioalcohols". Biofuel.org.uk. Retrieved 2014-04-16
43. http://www.inchem.org/documents/ehc/ehc/ehc102.htm
44. Schlaf M., Ghosh P., Fagan P.J., Hauptman E., Bullock R.M., Catalytic Deoxygenation
of 1,2-Propanediol to Give n-Propanol, Advanced Synthesis & Catalysis, 2009, 351,
789 – 800
45. Amada Y., Koso S., Nakagawa Y., Tomishige K., Hydrogenolysis of 1,2-Propanediol
for the Production of Biopropanols from Glycerol, ChemSusChem, 2010, 3, 728–736
46. Foskey A.T.J., Heinekey D.M., Goldberg K.I., Partial Deoxygenation of 1,2-
Propanediol Catalyzed by Iridium Pincer Complexes, ACS Catalysis 2012, 2,
1285−1289
47. Kusunoki Y., Miyazawa T., Kunimori K., Tomishige K., Highly active metal–acid
bifunctional catalyst system for hydrogenolysis of glycerol under mild reaction
conditions, Catalysis Communications, 2005, 6, 645–649;
48. Furikado I., Miyazawa T., Koso S., Shimao A., Kunimori K., Tomishige K., Catalytic
performance of Rh/SiO2 in glycerol reaction under hydrogen, Green Chemistry, 2007,
9, 582–588 ;
49. Shinmi Y., Koso S., Kubota T., Nakagawa Y., Tomishige K., Modification of Rh/SiO2
catalyst for the hydrogenolysis of glycerol in water, Appl. Catal., B, 2010, 94, 318–326;
50. Gandarias I., Arias P.L., Requies J., Gu¨ emez M.B. , Fierro J.L.G., Hydrogenolysis of
glycerol to propanediols over a Pt/ASA catalyst: The role of acid and metal sites on
product selectivity and the reaction mechanism, Appl. Catal., B, 2010, 97, 248–256
51. Nakagawa Y., Ning X., Amada Y. , Tomishige K., Solid acid co-catalyst for the
hydrogenolysis of glycerol to 1,3-propanediol over Ir-ReOx/SiO2, Applied Catalysis
A: General, 2012, 433–434, 128–134
52. Feng J., Xu B., REVIEW: Reaction mechanisms for the heterogeneous hydrogenolysis
of biomass-derived glycerol to propanediols, Progress in Reaction Kinetics and
Mechanism, 2014, 39, 1, 1–15
163
53. Amada Y., Shinmi Y., Koso S., Kubota T., Nakagawa Y., Tomishige K., Reaction
mechanism of the glycerol hydrogenolysis to 1,3-propanediol over Ir–ReOx/SiO2
catalyst, Applied Catalysis B: Environmental, 2011, 105, 117-127
54. Qin L.Z., Aqueous-phase deoxygenation of glycerol to 1,3-propanediol over
Pt/WO3/ZrO2 catalysts in a fixed-bed reactor, Green Chemistry, 2010, 12, 1466–1472
55. Longjie L., Yanhua Z., Aiqin W., Tao Z., Mesoporous WO3 Supported Pt Catalyst for
Hydrogenolysis of Glycerol to 1,3-Propanediol, Chinese Journal of Catalysis, 2012, 33,
1257–1261
56. Chaminand J., Djakovitch L., Gallezot P., Marion P., Pinel C., Rosier C., Glycerol
hydrogenolysis on heterogeneous catalysts, Green Chemistry, 2004, 6, 359 – 361
57. Wang S., Liu H., Selective hydrogenolysis of glycerol to propylene glycol on Cu–ZnO
Catalysts, Catalysis Letters, 2007, 117, 1–2, 62-67
58. Huang L., Zhu Y.L., Zheng H.Y., Li Y.W., Zeng Z.Y., Continuous production of 1,2-
propanediol by the selective hydrogenolysis of solvent-free glycerol under mild
conditions, Journal of Chemical Technology and Biotechnology, 2008, 83, 1670-1675
59. Miyazawa T. et al., Glycerol conversion in the aqueous solution under hydrogen over
Ru/C + an ion-exchange resin and its reaction mechanism, J. Catal., 2006, 240, 213–
221
60. Ryneveld E.V. et al, A catalytic route to lower alcohols from glycerol using Ni-
supported Catalysts, Green Chem., 2011, 13, 1819-1827
61. Wang M. et al, Catalytic transformation of glycerol to 1-propanol by combining
zirconium phosphate and supported Ru catalysts, RSC Adv., 2016, 6, 29769–29778
62. Yu L. et al., Propylene from Renewable Resources: Catalytic Conversion of Glycerol
into Propylene, ChemSusChem, 2014, 7, 743 – 747
63. Sun D. et al, Efficient production of propylene in the catalytic conversion of glycerol,
Applied Catalysis B: Environmental, 2015, 174–175, 13–20
64. Nakagawa Y. et al., Heterogeneous catalysis of the glycerol hydrogenolysis,Catal. Sci.
Technol., 2011, 1, 179–190
65. Gascon J et al., Amino-based metal-organic frameworks as stable, highly active basic
catalysts, Journal of Catalysis, 2009, 261, 75-87
164
66. Wang S. S., Yang G. Y. , Recent Advances in Polyoxometalate-Catalyzed Reactions,
Chem. Rev., 2015, 115, 11, 4893–4962
67. Brückman K., Che M., Haber J., On the physicochemical and catalytic properties of
H5PV2MoloO40 supported on silica, J. M. Tatibouët, Catal. Lett., 1994, 25, 225-240
68. Trolliet A., G. Coudurier, J. C. Vedrine, Influence of the nature and porosity of different
supports on the acidic and catalytic properties of H3PW12O40, Topics in Catal., 2001,
15, 73-81
69. E. Lopez-Salinas, J. G. Hernandez-Cortez, I. Schifer, E. Torres-Garcia, J. Navarrete, A.
Gutierrez-Carrillo, T. Lopez, P. P. Lottici, D. Bersani, Thermal stability of 12-
tungstophosphoric acid supported on zirconia, Appl. Catal. A: General, 2000, 193 , 215
70. Zhou Y., Guo Z., Hou W., Wang Q. and Wang J., Polyoxometalate-based phase transfer
catalysis for liquid–solid organic reactions: a review, Catal. Sci. Technol., 2015, 5,
4324-4335
71. Misono M., Unique acid catalysis of heteropoly compounds(heteropolyoxometalates)
in the solid state, Chem. Commun., 2001, 1141–1152
72. Atia H., Armbruster U., Martin A., Influence of alkaline metal on performance of
supported silicotungstic acid catalysts in glycerol dehydration towards acrolein , Appl.
Catal. A: Gen., 2011, 393, 331–339
73. Martin A., U. Armbruster, H. Atia, Recent developments in dehydration of glycerol
toward acrolein over heteropolyacids, Eur. J. Lipid Sci. Technol., 2012, 114, 10–23
74. Liu L., Ye X.P., Bozell J.J., A Comparative Review of Petroleum-Based and Bio-Based
Acrolein Production, ChemSusChem, 2012, 5 2012, 1162–1180
75. Katryniok A., S. Paul, F. Dumeignil, Recent Developments in the Field of Catalytic
Dehydration of Glycerol to Acrolein, ACS Catal., 2013, 3, 1819–1834
76. Hanan Atia, Udo Armbruster, Andreas Martin, Dehydration of glycerol in gas phase
using heteropolyacid catalysts as active compounds, Journal of Catalysis, 2008, 258,
71–82
77. Zhu S., Zhu Y., Hao S., Chen L., Zhang B. and Li Y., Aqueous-Phase Hydrogenolysis
of Glycerol to 1,3-propanediol Over Pt-H4SiW12O40/SiO2, Catalysis Letters, 2012, 142,
267–274
165
78. Zhu S., Zhu Y., Hao S., Zheng H., Mo T., Li Y., One-step hydrogenolysis of glycerol
to biopropanols over Pt–H4SiW12O40/ZrO2 catalysts, Green Chemistry, 2012, 14, 2607-
2616
79. Zhu S., Qiu Y., Zhu Y., Hao S., Zheng H., Li Y., Hydrogenolysis of glycerol to 1,3-
propanediol over bifunctional catalysts containing Pt and heteropolyacids, Catalysis
Today, 2013, 212, 120– 126
80. Cavani F, Guidetti S, Marinelli L, Piccinini M, Ghedini E, Signoretto M, The control
of selectivity in gas-phase glycerol dehydration to acrolein catalysed by sulfated
zirconia, Applied Catalysis B: Environmental, 2010, 100, 197–204
81. Alhanash A., Kozhevnikova E.F., Kozhevnikov I.V., Hydrogenolysis of Glycerol to
Propanediol Over Ru: Polyoxometalate Bifunctional Catalyst, Catalysis Letters, 2008,
120, 307-311
82. Gong L., Selective hydrogenolysis of glycerol to 1,3-propanediol over a
Pt/WO3/TiO2/SiO2 catalyst in aqueous media, Applied Catalysis A: General, 2010, 390,
119–126
83. Zhang Y., Zhao X.C., WangY., Zhou L., Zhang J., Wang J., Wang A., Zhang T.,
Mesoporous Ti–W oxide: synthesis, characterization, and performance in selective
hydrogenolysis of glycerol, Journal of Materials Chemistry A, 2013, 1, 3724–3732
84. Oh J., Dash D., Lee H. Selective conversion of glycerol to 1,3-propanediol using Pt-
sulfated zirconia, Green Chemistry, 2011, 13, 2004-2007
85. Alhanash A., Kozhevnikova E.F., Kozhevnikov I.V., Gas-phase dehydration of glycerol
to acrolein catalysed by caesium heteropoly salt, Applied Catalysis A: General, 2010,
378, 11-18
86. Zhu S., Gao X., Zhu Y., Xiang X., C. Hu, Li Y., Alkaline metals modified Pt–
H4SiW12O40/ZrO2 catalysts for the selective hydrogenolysis of glycerol to 1,3-
propanediol, Applied Catalysis B: Environmental, 2013, 140–141, 60– 67
87. Kongpatpanich K., T. Nanok, B. Boekfa, M. Probst, J. Limtrakul, Structures and
reaction mechanisms of glycerol dehydration over H-ZSM-5 zeolite: a density
functional theory study, Physical Chemistry Chemical Physics, 2011, 13, 6462–6470
88. Kurosaka T., Production of 1,3-propanediol by hydrogenolysis of glycerol catalyzed by
Pt/WO3/ZrO2, Catalysis Communications, 2008, 9, 1360–1363
166
89. Pope M.T., “Heteropoly and Isopoly Oxometallates.” Springer-Verlag, Berlin, 1983
90. Barton D.G., Soled S.L., Meitzner G.D., Fuentes G.A., Iglesia E., Structural and
Catalytic Characterization of Solid Acids Based on Zirconia Modified by Tungsten
Oxide, Journal of Catalysis 1999, 181, 57–72
91. Petkovic L. M., Bielenberg J. R. , Larsen G.,, A Comparative Study of n-Pentane and
n-Butane Isomerization over Zirconia-Supported Tungsten Oxide: Pulse and Flow
Studies and DRIFTS Catalyst Characterization J. Catal., 1998, 178, 533-539
92. Misono M., Recent progress in the practical applications of heteropolyacid and
perovskite catalysts: Catalytic technology for the sustainable society, Catalysis Today,
2009, 144, 285–291
93. Kozhevnikov I.V., Heterogeneous acid catalysis by heteropoly acids: Approaches to
catalyst deactivation, Journal of Molecular Catalysis A: Chemical, 2009, 305, 104–111
94. Ferreira P., Fonseca I.M., Ramos A.M., Vital J., Castanheiro J.E., Valorisation of
glycerol by condensation with acetone over silica-included heteropolyacids, Applied
Catalysis B: Environmental, 2010, 98, 94–99
95. Timofeeva M.N., Acid catalysis by heteropoly acids, Applied Catalysis A: General,
2003, 256, 19-35
96. Jin H., Yi X., Sun X., Qiu B., Fang W., Weng W., Wan H., Influence of H4SiW12O40
loading on hydrocracking activity of non-sulfide Ni–H4SiW12O40/SiO2 catalysts, Fuel,
2010, 89, 1953-1960
97. Xu S., Wang L., Chu W., Yang W., Influence of Pd precursors on the catalytic
performance of Pd– H4SiW12O40/SiO2 in the direct oxidation of ethylene to acetic acid,
Journal of Molecular Catalysis A: Chemical, 2009, 310, 138–143
98. Mizugaki T., Yamakawa T., Arundhathi R., Mitsudome T., Selective Hydrogenolysis
of Glycerol to 1,3-Propanediol Catalyzed by Pt Nanoparticles AlOx/WO3, Catalysis
Letters, 2012, 41, 1720-1722
99. Dam J.T., Djanashvili K, Kapteijn F., Hanefeld U., Pt/Al2O3 Catalyzed 1,3-Propanediol
Formation from Glycerol using Tungsten Additives, ChemCatChem, 2013, 5, 497 – 505
100. Arundhathi R., Mizugaki T.,Mitsudome T.,Jitsukawa K., Kaneda K., Highly Selective
Hydrogenolysis of Glycerol to 1,3-Propanediol over a Boehmite-Supported
Platinum/Tungsten Catalyst, ChemSusChem, 2013, 6, 1345 – 1347
167
101. Delgado S. N., Influence of the nature of the support on the catalytic properties of Pt-
based catalysts for hydrogenolysis of glycerol, Journal of Molecular Catalysis A:
Chemical, 2013, 367, 89– 98
102. Zhu S., Gao X., Zhua Y., Cuia J., Zheng H., Li Y., SiO2 promoted Pt-WOx/ZrO2
catalysts for the selective hydrogenolysis of glycerol to 1,3-propanediol, Applied
Catalysis B: Environmental 2014, 158–15, 391–399
103. Deng C., Duan X., Zhou J., Chen D., Zhou X., Yuan W., Size effects of Pt-Re bimetallic
catalysts for glycerol hydrogenolysis, Catalysis Today, 2014, 234, 208–214
104. Vanama P. K., Kumar A., Ginjupalli S. R., Komandur V.R.C, Vapor-phase
hydrogenolysis of glycerol over nanostructured Ru/MCM-41 catalysts, Catalysis
Today, 2015, 250, 226–238
105. Huang L., Zhu Y., Zheng H., Ding G., Li Y., Direct conversion of Glycerol into 1,3-
Propanediol over Cu-H4SiW12O40/SiO2, Catalysis Letters, 2009, 131, 312–320
106. Feng Y. Yin H., Wang A., Shen L., Yu L., Jiang T., Gas phase hydrogenolysis of
glycerol catalyzed by Cu/ZnO/MOx (MOx =Al2O3, TiO2, and ZrO2) catalysts, Chemical
Engineering Journal, 2011, 168, 403–412
107. Nakagawa Y., Shinmi Y., Koso S., Tomishige K., Direct hydrogenolysis of glycerol
into 1,3-propanediol over rhenium-modified iridium catalyst, Journal of Catalysis,
2010, 272, 191–194
108. Thibault M.E., DiMondo D. V., Jennings M., Abdelnur P. V., Eberlin M. N., Schlaf M.,
Cyclopentadienyl and pentamethylcyclopentadienyl ruthenium complexes as catalysts
for the total deoxygenation of 1,2-hexanediol and glycerol, Green Chemistry, 2011, 13,
357-366
109. Perosa A., Tundo P., Selective Hydrogenolysis of Glycerol with Raney Nickel,
Industrial & Engineering Chemistry Research, 2005, 44, 8535-8537
110. Yu W., Xu J., Ma H., Chen C., Zhao J., Miao H., Song Q., A remarkable enhancement
of catalytic activity for KBH4 treating the carbothermal reduced Ni/AC catalyst in
glycerol hydrogenolysis, Catalysis Communications, 2010, 11, 493-497
111. Zheng Z., Wang J., Lu Z., Luo M., Zhang M., Xu L., Ji J., Hydrogenolysis of 2-
Tosyloxy-1,3-propanediol into 1,3-Propanediol over Raney Ni Catalyst, Journal of the
Brazilian chemical society, 2013, 24, 3, 385-391
168
112. Komplin G.C, Smegal J.A., Hydrogenation catalyst and hydrogenation method, US
Pat., 7 335 800 B2, 2008
113. Peng G., Wang X., Chen X., Jiang Y., Mu X., Zirconia-supported niobia catalyzed
formation of propanol from 1,2-propanediol via dehydration and consecutive hydrogen
transfer, J. Ind. Eng. Chem., 2014, 20, 2641–2645.
114. Lebugle A., Axelsson U., Nyholm R., Martensson N. Phys. Scripta 1981, 23, 825
115. Wachs, I.E., Fitzpatrick, L.E., “Characterization of Catalytic Materials”, Manning
Publications Co., 1992, Greenwich
116. Wang F. et al., Catalytic dehydration of glycerol over vanadium phosphate oxides in
the presence of molecular oxygen, J. Catal., 2009, 268, 260–267
117. Hao S. L. et al, Hydrogenolysis of glycerol to 1,2-propanediol catalyzed by Cu-
H4SiW12O40/Al2O3 in liquid phase, J Chem Technol Biotechnol, 2010, 85, 1499–1503
118. Tsunoda T., Nomura K., Process for producing 1,3-propanediol, US Pat., 6 911 566 B2,
2005
119. Arntz D., Haas T., Schafer-sindlinger A., Process for the preparation of 1,3-propanediol
by the hydrogenation of hydroxypropionaldehyde, U.S. Patent No. 5 364 984, 1994
120. Hatch L.F., Evans T.W., Process for hydrating olefinic aldehydes, U.S. Patent No. 2
434 110, 1948
121. Haas T., Wiegand N., Arntz D., Process for the production of 1,3-propanediol, U.S.
Patent No. 5 334 778, 1994
122. Lin X. et al, Hydrogenolysis of Glycerol by the Combined Use of Zeolite and Ni/Al2O3
as Catalysts: A Route for Achieving High Selectivity to 1‑Propanol; Energy Fuels 2014,
28, 3345−3351
123. T. Okuhara, T. Nishimura, H. Watanabe, K. Na, M. Misono, Novel Catalysis of Cesium
Salt of Heteropoly Acid and its Characterization by Solid-state NMR, Stud. Surf. Sci.
Catal., 1994, 90, 419–428
124. T. Okuhara and T. Nakato, Catalysis by porous heteropoly compounds, Catal. Surv.
JPN, 1998, 2, 1, 31–44
125. He, W. Huang, J. Liu, Q. Zhu, Condensation of formaldehyde and methyl formate to
methyl glycolate and methyl methoxy acetate using heteropolyacids and their salts,
Catal. Today, 1999, 51, 127–134
169
126. Haber J., Pamin K., Matachowski L., Napruszewska B., Poltowicz J., “Potassium and
Silver Salts of Tungstophosphoric Acid as Catalysts in Dehydration of Ethanol and
Hydration of Ethylene”, Journal of Catalysis, 2002, 207, 296–306
127. Soled, S., Miseo, S., McVicker, G., Gates, W.E., Gutierrez, A., Paes, J.,“Preparation of
bulk and supported heteropolyacid salts”, Catalysis Today, 1997, 36,441-450, 42
128. Kozhevnikov, I.V., “Fine organic synthesis with the aid of heteropolycompounds”,
Russian Chemical Reviews, 1993, 62, 5, 473-491.
129. Okuhara T., Watanabe H., Nishimura T., Inumaru K., Misono M., Microstructure of
Cesium Hydrogen Salts of 12-Tungstophosphoric Acid Relevant to Novel Acid
Catalysis, Chem. Mater., 2000, 12, 2230–2238
130. Friesen D.A., Gibson D.B., Langford C.H., Heterogeneous Cs3PW12O40 photocatalysts,
Chem. Commun., 1998, 543–544
131. Rana S, Mallick S, Rath D, Parida KM, Characterization of novel Cs and K substituted
phosphotungstic acid modified MCM-41 catalyst and its catalytic activity towards
acetylation of aromaticalcohols, J Chem Sci, 2012, 124, 1117–1125
132. Dias JA, Caliman E, Dias SCL, Effects of cesium ion exchange on acidity of 12
tungstophosphoric acid. Microporous Mesoporous Mater, 2004, 76, 221–232
133. Izumi Y., Ogawa M., Urabe K., Alkali metal salts and ammonium salts of Keggin-type
heteropoly acids as solid acid catalysts for liquid-phase Friedal–Crafts reactions. Appl
Catal A Gen, 1995, 132, 127–140
134. Okuhara T., Nishimura T., Misono M., Novel Microporous Solid "Superacids":CsxH3-x
PW12O40 (2<x<3), 1l th International Congress on Catalysis - 40th Anniversary, Studies
in Surface Science and Catalysis, 1996, 101, 581-590
135. Essayem N. et al, Acidic and catalytic properties of CsxH3-x PW12O40 heteropolyacid
compounds, Catalysis Letters, 1995, 34 , 223-235
136. Bardin B.B., Davis R.J., Heteropolyacid and sulfated zirconia catalysts, Topics in
Catalysis, 1998, 6, 77–86
137. Ezzat Rafiee et al, Cesium Salts of Phosphotungstic Acid: Comparison of Surface
Acidity, Leaching Stability and Catalytic Activity for the Synthesis of â-Ketoenol
Ethers, S. Afr. J. Chem., 2013, 66, 145–149
170
138. Shaimaa M. Ibrahim, Catalytic Activity and Selectivity of Unsupported
Dodecatungstophosphoric Acid, and Its Cesium and Potassium Salts Supported on
Silica, Modern Research in Catalysis, 2013, 2, 110-118
139. K. Narasimharao et al., Structure–activity relations in Cs-doped heteropolyacid
catalysts for biodiesel production, Journal of Catalysis, 2007, 248, 226–234
140. Pesaresia L., Brown D.R., Lee A.F., Montero J.M., Williams H., Wilson K., Cs-doped
H4SiW12O40 catalysts for biodiesel applications, Applied Catalysis A: General, 2009,
360, 50–58
141. Sujiao F et al, Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide
over Cesium Salts of Keggin-type Heteropoly Acids, Acta Chim. Sinica, 2012, 70,
2316-2322
142. Haider M.H., Dummer N. F., Zhang D., Miedziak P., Davies T. E., Taylor S. H.,
Willock D. J., Knight D. W., Chadwick D., Hutchings G. J., Rubidium- and caesium-
doped silicotungstic acid catalysts supported on alumina for the catalytic dehydration
of glycerol to acrolein, Journal of Catalysis, 2012, 286, 206–213
143. Li X. K., Zhao J., Ji W. J., Zhang Z. B., Chen Y., Au C. T., Hanc S., Hibst H., Effect of
vanadium substitution in the cesium salts of Keggin-type heteropolyacids on propane
partial oxidation, J. Catal., 2006, 237, 58-66
144. Kamiya Y, Okuhara T, Misono M, Miyaji A, Tsuji K, Nakajo T. Catalytic Chemistry
of Supported Heteropolyacids and Their Applications as Solid Acids to Industrial
Processes, Catal Surv from Asia, 2008, 12, 101-113
145. Bhatt N., Patel A., Esterification of 1° and 2° alcohol using an ecofriendly solid acid
catalyst comprising 12-tungstosilicic acid and hydrous zirconia, J. Mol. Catal., 2005,
238, 223-228.
146. Guo X. et al , Effect of cesium content on the structure and catalytic performances of
heteropoly compounds in one-step synthesis of methylmethacrylate from methacrolein,
Korean J. Chem. Eng., 2008, 25, 697-702
147. Langpape M., Millet J. M. M., Ozkan U. S., Boudeulle M., Study of Cesium or Cesium-
Transition Metal-Substituted Keggin-Type Phosphomolybdic Acid as Isobutane
Oxidation Catalysts: I. Structural Characterization, J. Catal., 1999, 181, 8
171
148. Maris E. P., Davis R. J., Hydrogenolysis of glycerol over carbon-supported Ru and Pt
catalysts. J. Catal., 2007, 249 , 328–337
149. Montassier C., Ménézo J.C., Hoang L.C., Renaud C., Barbier J., Aqueous polyol
conversions on ruthenium and on sulfur-modified ruthenium, J. Mol. Catal., 1991, 70,
99-110
150. Wang K., Hawley M. C., Furney T. D., Mechanism Study of Sugar and Sugar Alcohol
Hydrogenolysis Using 1,3-Diol Model Compounds, Ind. Eng. Chem. Res., 1995, 34,
3766−3770
151. Auneau F., Michel C., Delbecq F., Pinel C., Sautet P., Unravelling the mechanism of
glycerol hydrogenolysis over rhodium catalyst through combined experimental-
theoretical investigations, Chem. A Eur. J., 2011, 17, 50, 14288−14299
152. Ramachandran P. A., Chaudhari R. V., Three Phase Catalytic Reactors; Gordon and
Breach Science Publishers: New York, 1983.
153. Fundamentals of Reaction Engineering, Rafael Kandiyoti, 2009
154. Wang M., Catalytic transformation of glycerol to 1-propanol by combining zirconium
phosphate and supported Ru catalysts, RSC Adv., 2016, 6, 29769-29778
155. Dasari M. A., Catalytic Conversion of Glycerol and Sugar Alcohols to Value-Added
Products. Ph.D. Thesis, University of Missouri-Columbia, Columbia, MO, USA, 2006.
156. Karwowska B., Solid State Electrochemical Characterization of Tungsten Oxides and
Related Heteropoly-12-Tungstic Acid Single Crystals, Electroanalysis, 1995, 7, 11,
1005-1009
157. Misono M. Heterogeneous Catalysis by Heteropoly Compounds of Molybdenum and
Tungsten, 'catal. Rev., Sci Eng, 1987, 29, 269-321
158. Lan L.W., Li J., Chen Q.Y., Photocatalytic Properties for Photocatalytic Water Splitting
of H4SiW12O40/TiO2, Nonferrous Metals, 2009, 3, 35-38
159. Chia M et al, Selective Hydrogenolysis of Polyols and Cyclic Ethers over Bifunctional
Surface Sites on Rhodium–Rhenium Catalysts. Journal of the American Chemical
Society, 2011, 133, 32, 12675-12689
160. Aramendía M. A. et al., Liquid-phase heterogeneous catalytic transfer hydrogenation of
citral on basic catalysts. Journal of Molecular Catalysis A: Chemical, 2001, 171, 1-2,
153-158
172
161. Schlaf M., Selective deoxygenation of sugar polyols to α,ω-diols and other oxygen
content reduced materials-a new challenge to homogeneous ionic hydrogenation and
hydrogenolysis catalysis. Dalton Transactions, 2006, 39, 4645-4653
162. Braga T. P. et al., Gas-Phase Conversion of Glycerol to Acetol: Influence of Support
Acidity on the Catalytic Stability and Copper Surface Properties on the Activity; J. Braz.
Chem, Soc., 2016, 00, 00, 1-11
163. Coll D. et al., Stability of intermediates in the glycerol hydrogenolysis on transition
metal catalysts from first principles, Phys. Chem. Chem. Phys., 2011, 13, 1448-1456
164. Dam J. T., Renewable Chemicals: Dehydroxylation of Glycerol and Polyols,
ChemSusChem, 2011, 4, 1017 – 1034
165. Auneau F. et al., Unravelling the Mechanism of Glycerol Hydrogenolysis over
Rhodium Catalyst through Combined Experimental–Theoretical Investigations, Chem.
Eur. J., 2011,17, 14288 – 14299.
166. Wawrzetz A. et al., Towards understanding the bifunctional hydrodeoxygenation and
aqueous phase reforming of glycerol, J. Catal., 2010, 269, 411–420;
167. Gascon J et al., Amino-based metal-organic frameworks as stable, highly active basic
catalysts, Journal of Catalysis, 261 (2009) 75-87.
168. Misono M. et al, catalysis by heteropoly compounds, successful design of catalysis,
Amsterdam,Elsevier Science publisher, 1988, 267-278;
169. Misono M., Mizuno N., Katamura K., Kasai A., Konishi Y., Sakata K., Okuhara T.,
Yoneda Y., Catalysis by heteropoly compounds. III: The struture and properties of 12
hetoropolyacids of molybdenum and tungsten and their salts pertinantto heterogeneous
catalysis, Bull. Chem. Soc Jpn. 1982, 55, 400-406
170. Kozhevnikov I. V., Catalysis by Heteropoly Acids and Multicomponent
Polyoxometalates in Liquid-Phase Reactions, Chem. Rev., 1998, 98, 171-198
171. Liu L. et al. Supported H4SiW12O40/Al2O3 solid acid catalysts for dehydration of
glycerol to acrolein: Evolution of catalyst structure and performance with calcination
temperature / Applied Catalysis A: General, 2015, 489, 32–41
172. a. Hernández-Cortez J.G.et al, Study of acid–base properties of supported heteropoly
acids in thereactions of secondary alcohols dehydration, Catalysis Today, 2014, 220–
173
222, 32– 38; b. D. Zhang et al., Dehydration of 1,2-propanediol to propionaldehyde
over zeolite catalysts, Applied Catalysis A: General, 2011, 400, 148–155
173. Thomas A., Dablemont C., Basset J. M. , Lefebvre, F. Comparison of H3PW12O40 and
H4SiW12O40 heteropolyacids supported on silica by 1H MAS NMR, C. R. Chim.,
2005, 8, 1969–1974
174. Deltcheff C. R., Fournier M., Franck R. , Thouvenot R., Vibrational Investigations of
Polyoxometalates. 2. Evidence for Anion-Anion Interactions in Molybdenum(V1) and
Tungsten(V1) Compounds Related to the Keggin Structure, Inorg. Chem., 1983, 22,
207-216
175. Ressler T., Timpe O., Girgsdies F., Wienold J., Neisius T., In situ investigations of the
bulk structural evolution of vanadium-containing heteropolyoxomolybdate catalysts
during thermal activation, J. Catal., 2005, 231, 2, 279–291
176. Janik M.J., Bardin B.B., Davis R.J., Neurock M.A., A Quantum Chemical Study of the
Decomposition of Keggin-Structured Heteropolyacids, J. Phys. Chem. B, 2006, 110, 9,
4170–4178
177. Watzenberger O., Emig G. , Lynch D. T , Oxydehydrogenation of isobutyric acid with
heteropolyacid catalysts: Experimental observations of deactivation, J. catal. 1990, 124,
247-258
178. Rafiee, M. Joshaghani and P. Ghaderi-Shekhi Abadi, Synthesis and characterization of
carbon@HPW core/shell nanorod using potato as a novel precursor: Efficient catalyst
for C–N coupling reaction, Arabian J. Chem., 2015
179. Biju M. Devassy et al., Zirconia-supported heteropoly acids: Characterization and
catalytic behavior in liquid-phase veratrole benzoylation, Journal of Catalysis, 2005,
236, 313–323
180. Liu L., Wang B., Du Y., Zhong Z., Borgna A., Bifunctional
Mo3VOx/H4SiW12O40/Al2O3 catalysts for one-step conversion of glycerol to acrylic
acid: Catalyst structural evolution and reaction pathways, Appl. Catal., B, 2015, 174–
175, 1-12
181. a. Sawant-Dhuri D., Balasubramanian V. V., Ariga K., Park D. H., Choy J. H., Cha W.
S., Al-deyab S. S., Halligudi S. B., Vinu A., Titania Nanoparticles Stabilized HPA in
SBA-15 for the Intermolecular Hydroamination of Activated Olefins, ChemCatChem,
174
2014, 6, 3347; b. T. Okuhara, N. Mizuno, M. Misono, Catalytic Chemistry of
Heteropoly Compounds, Adv. Catal., 1996, 41, 113
182. Parida K.M., Mallick S., Silicotungstic acid supported zirconia: An effective catalyst
for esterification reaction, Journal of Molecular Catalysis A: Chemical, 2007, 275, 77–
83
183. Phuruangrat A, Ham DJ, Hong SJ, Thongtem S, Lee JS. Synthesis of hexagonal WO3
nanowires by microwaveassisted hydrothermal method and their electrocatalytic
activities for hydrogen evolution reaction, J. Mater. Chem., 2010, 20, 1683-1690
184. Zhao Y, Fan H, Li W, Bi L, Wang D, Wu L. Incorporation of polyoxotungstate
complexes in silica spheres and in situ formation of tungsten trioxide nanoparticles.
Langmuir., 2010, 26, 18, 14894–14900
185. Bai S et al, Synthesis mechanism and gas-sensing application of nanosheet-assembled
tungsten oxide microspheres, J. Mater. Chem. A, 2014, 2, 7927–7934
186. Katumba G, Mwakikunga BW. FTIR and Raman spectroscopy of carbon nanoparticles
in SiO2, ZnO and NiO matrices. Nanoscale Res Lett., 2008, 3, 11, 421–426
187. Priya S.S et al, Metal–acid bifunctional catalysts for selective hydrogenolysis ofglycerol
under atmospheric pressure: A highly selective route toproduce propanols, Applied
Catalysis A: General, 2015, 498, 88–98
188. Mauriello F., Ariga H., Musolino M.G., Pietropaolo R., Takakusagi S., Asakura K.,
Exploring the catalytic properties of supported palladium catalysts in the transfer
hydrogenolysis of glycerol. Appl. Catal. B, 2015, 166–167, 121–131
189. A. Laurance B, Bright NPRA Annual meeting, Am-91 53, 1995; B. Wang J. S., Li B.
L., Xu X. Z., Ke, X. M., High metal tolerance matrix for FCC catalyst, Fluid cracking
catalyst, 111-119; C. Travers C., Isomerization of light paraffins, Petroleum refining.
Vol.3. Conversion Processes.
190. Shi C., Wang R., Zhu G., Qiu S., Long J., Synthesis, characterization, and catalytic
properties of SiPW-X mesoporous silica with heteropolyacid encapsulated into their
framework, European Journal of Inorganic Chemistry, 2005, 4801-4807
191. Dufaud V., Lefebvre F., Niccolai G.P., Aouine M., New insights into the encapsulation
and stabilization of heteropolyacids inside the pore walls of mesostructured silica
materials, Journal of Materials Chemistry, 2009, 19, 1142-1150
175
192. Atia H., Armbruster U., Martin A., Dehydration of glycerol in gas phase using
heteropolyacid catalysts as active compounds. DGMK Tagungsbericht, 2008. 2008-3
(Preprints of the DGMK-Conference "Future Feedstocks for Fuels and Chemicals"),
2008, 177-184.
193. Beck J. S., Vartuli J. C., Roth W. J., Leonowicz M. E, Kresge C. T., Schmitt K. D., Chu
C. T-W., Olson D. H., Sheppard E. W., McCullen S. B., Higgins J. B.,Schlenker J. L.,
“A new family of mesoporous molecular sieves prepared with liquid crystal templates”,
Journal of American Chemical Society, 1992, 27, 10834-10843
194. Liu Q., Wu W., Wang J., Ren X., Wang Y., “Characterization of 12-tungstophosphoric
acid impregnated on mesoporous silica SBA-15 and its catalytic performance in
isopropylation of naphthalene with isopropanol”, Microporous and Mesoporous
Materials, 2004, 76, 51-60
195. Jha A., Garade A. C., Mirajkar S. P., Rode C. V., MCM-41 supported phosphotungstic
acid for the hydroxyalkylation of phenol to phenolphthalein Ind. Eng. Chem. Res.,
2012, 51, 3916
196. Kozhevnikov I.V., Sinnema A., Jansen R.J.J., Pamin K., Bekkum H., New acid catalyst
comprising heteropoly acid on a mesoporous molecular sieve MCM-41, Catal. Lett.,
1994, 30, 241-252
197. Satterfield C.N., Heterogeneous Catalysis in Industrial Practice, 2nd ed., McGraw-Hill,
New York, 1991, p. 123
198. Arco M. del, Caballero A., Malet P., Rives V., Effect of consecutive and alternative
oxidation and reduction treatments on the interactions between titania (anatase and
rutile) and copper, J. Catal., 1998, 113, 120-128
199. Lingaiah N. et al, Influence of Vanadium Location in Titania Supported
Vanadomolybdophosphoric Acid Catalysts and Its Effect on the Oxidation and
Ammoxidation Functionalities, J. Phys. Chem. C 2008, 112, 8294–8300
200. Rosa María Ladera et al., TiO2-supported heteropoly acid catalysts for dehydration of
methanol to dimethyl ether: relevance of dispersion and support interaction, Catal. Sci.
Technol., 2015, 5, 484–491
176
201. Ladera R. M., Fierro J. L. G., Ojeda M. and Rojas S., TiO2-supported heteropoly acids
for low-temperature synthesis of dimethyl ether from methanol, J. Catal., 2014, 312,
195–203
202. Thamaphat K., Phase Characterization of TiO2 Powder by XRD and TEM, Kasetsart J.
(Nat. Sci.), 2008, 42, 357 - 361
203. Buck E. C., Arey B. W., Fiskum S. K., Geeting J. G. H., Jenson E. D., McNamara B.
K., Poloski A. P., Identification of Washed Solids from Hanford Tanks 241-AN-102
and 241-AZ-101 with X-Ray Diffraction, Scanning Electron Microscopy, and Light-
Scattering Particle Analysis, WTP Project Report, 2003
204. Park H., Yun Y. S., Kim T. Y., Lee K. R., Baek J., J. Kinetics of the dehydration of
glycerol over acid catalysts with aninvestigation of deactivation mechanism by coke,
Applied Catalysis B: Environmental, 2015, 176, 1–10
205. Kim Y.T., You S.J., Jung K.D., Park E.D., Effect of Al Content on the Gas-Phase
Dehydration of Glycerol over Silica-Alumina-Supported Silicotungstic Acid Catalysts,
Bull. Korean Chem. Soc., 2012, 33, 2369–2377
206. Bühler W., Dinjus E., Ederer H.J., Kruse A., Mas C., J. Y, Supercrit. Fluids, 2002, 22,
37–53
207. Tsukuda E., Sato S., Takahashi R., Sodesawa T., Production of acrolein from glycerol
over silica-supported heteropoly acids, Catal. Commun., 2007, 8, 1349–1353
208. Yun D., . Yun S., Kim T. Y., Park H., Lee J. M., Han J. W., Yi J., Mechanistic study of
glycerol dehydration on Brønsted acidic amorphous aluminosilicate, Journal of
Catalysis, 2016, 341, 33–43
209. Jia Wang, Xiaochen Zhao, Nian Lei, Lin Li, Leilei Zhang, Shutao Xu, Shu Miao, Xiaoli
Pan, Aiqin Wang, Tao Zhang, Hydrogenolysis of Glycerol to 1,3-propanediol under
Low Hydrogen Pressure over WOx-Supported Single/Pseudo-Single Atom Pt Catalyst,
ChemSusChem, 2016, 9, 784 – 790
177
Appendix A Literature Data
Table A-1 Summary of Reported Catalysts and Reaction Conditions for Converting Glycerol into 1,3-PD in batch reactor
Catalyst Catatyst
loading, wt%
Glycerol
content,
wt%
Temp.
oC
Press.
Mpa
React.
Time, h
Conv
%
Selectivity Reference
1,3PD 1,2PD 1-PO
1 Cu/SiO2 0.6 40(n-
butanol)
240 8 5 20 2 92 - Vasiliadou
E. S. et al.
(2014)
2 5Pt-Re/CNTs 14µmol
Pt/0.2gGl
1 170 4 8 55 26 52 26.0 Chenghao
Deng et al.,
(2014) 3
Ir-ReOx/SiO2 3.75 66.7 120 8
24 38.6 59 9.4 24.4 Tamura M.,
(2014) Ir-ReOx/SiO2 None H2SO4
9.4 66.2 11.9 15.8
H+/Ir = 1 23 57.7 7.9 27.0
4 1Ru/SBA‐15(H2‐500) 3.75 40 160 8 8 4 7.2 44 19.8 Li Y. et al.,
(2014) 5Ru/SBA‐15(Air‐300/H2‐300) 12.4 4.1 29 21.8
5 Ru/Al2O3 3.75 Ru/Al2O3,
3.55HZSM 40
160 8 8
18 1.7 30.5 17.7
(1+2)
Li Y. et al.,
(2014) Ru/HZSM5(360) 3.75 19 4 27.2 28.0
Ru/Al2O3 + HZSM5(25) 3.75 Ru/Al2O3,
3.55HZSM
120 6.4 6.2 36 20.4
6 5Pd–5Re/Al2O3 3.75 40 200 8 18 23.6 13.6 54.5 26.6 Li Y. et al.,
(2014) 5Pd/Al2O3 3.3 9.9 63.3 19.3
7
Pt/Ti100W0
25 10 180 5.5 12
7.8 7.2 83 9.6 Zhang Y.,
(2013)
Pt/Ti90W10 18.4 40.3 13..7 32.5
Pt/Ti80W20 24.2 33.5 11.6 36.6
Pt/Ti50W50 6.7 40.9 7.2 44.3
8 Pt/Al2O3+STA 0.5mol% 200 4 18 49 28 3 31.0 Dam J.T.,
(2013) 9 Pt/WOx/AlOOH 108.6 3 180 5 12 100 66 2 11.0 Arundhathi
R.(2013) Pt/TiO2 24 0 61.8 6.2(1+2)
178
10 Pt/Al2O3 22 4.5 210 6 6 10 12.1 33.8 2.6 Delgado S.
N., (2013)
11 PtAlOx/WO3
108.6 3 180 3 10 90 44 2.2 37.8 Mizugaki
T., (2012) PtMnOx/WO3 87 33 1.14 48.3
PtZrOx/WO3 87 33 3.45 48.3
12 Ir-ReOx/silica–alumina 3.75 20 120 8 24 31.5 59.8 13.3 17.7 Nakagawa
Y. et al.,
(2012)
13 Rh–MoOx/SiO2 1.4 20 120 8
(initial)
4 7.1 9.6 41 34.0 Koso S. et
al., (2012) Rh–ReOx/SiO2 9.7 21 32 31.0
14 Pt/m-WO 10 25 180 5.5 12 18 39.3 4.1 33.8 Longjie L.,
(2012) Pt/c-WO3 4.5 29.9 14.1 23.6
15
Pt-Sulfated ZrO2
12
57 (water)
170 7.3
(initial) 24
62.9 12.3 32.1 0.0
Jinho Oh
(2011)
Pt-Sulfated ZrO2
57 (in
DMI)
66.5 55.6 2.9 0.0
Fe-Sulfated ZrO2 51.4 13.8 0 0.0
Mn-Sulfated ZrO2 56.4 14.5 0 0.0
Pt/STA/ZrO2 50.2 17.2 5.4 0.0
Pt/PTA/ZrO2 48.4 15.4 3.8 0.0
16 Pt/WO3/TiO2/SiO2 2ml/40ml 10 180 5.5 12 15.3 50.5 9.2 25.1 Gong L.,
(2010) 17 Ir–ReOx/SiO2 3.75 + H2SO4 80 120 8 24 62.8 49 10 33.0 Nakagawa
Y. (2010) 18 Pt–Re/C Sintered (5.7 wt% Pt,
4.6 wt% Re)
Substrate/
surface metal
350:1(mol)
1 170 4 20 34 33 22.0 Daniel O.M.
et al. (2010) 19 Ru–Re/SiO2-r450 4 40 160 8 23.8 13.6 51.1 23.0 Ma L.
(2010) Ru–Re/SiO2-r200 51 8.3 49.1 26.1
20 Pt/WO3/ZrO2 10 170 5.5 Ethanol-
water
45.7 21.2 8 32.1 Leifeng G.
et al., (2009) Ethanol 38.2 23 13.6 46.6
Water 24.7 25.7 15 21.3
21 2Pt/19.6WO3/ZrO2 36 170 18 86 28 14.5 32.0
2Pt/19.6WO3/Al2O3 44 30 25 26.4
179
Pt/WO3/TiO2 57 (in
DMI)
8
(initial)
16.9 38.4 42 30.2 Kurosaka
T., (2008) 22 5% Rh/Cs2.5H0.5[PW12O40] 20 20 180 0.5 10 6.3 7.1 65.4 27.5 Alhanash
A., (2008) 5% Ru/Cs2.5H0.5[PW12O40] 23 0 73.6 4.3
23 Rh/SiO2 + Amberlystb 3.75 20 120 8
(initial)
10 14.3 9.8 26 42.2 Furikado I.
et al. (2007) 24 Ru/C+Amberlyst 4+8%amberlyst 20 120 8 10 12.9 4.9 55.4 14.1 Miyazawa
T., (2006) Rh/C+Amberlyst 3 9 32.7 40.4
25 Rh/C 20 4 initial
180
8 10 0.3 3.4 58.6 0.0 Kusunoki Y.
(2005) Rh/C + H2WO4 1.3 20.9 56.7 10.4
26
Rh/C (5%)
0.3 + H2WO4
19%
(sulfolane) 180 8 168
32 12 6 80.0 Chaminand
J. et al.
(2004)
Rh/Al2O3 (5%) 19% in
water
27 12 45 -
Rh/C (5%) 21 6 70 -
Rh/HY (3.5%) 3 0 0 100.0
180
Table A-2 Summary of Reported Catalysts and Reaction Conditions for Converting Glycerol into 1,3-PD in fix-bed reactor
Catalyst Catalyst
loading,
gr
Glycerol
w %
Temp.
oC
H2 flow
rate,
ml/min
Press.
Mpa
Conv. % Selectivity, % Reference
1,3-PD 1,2-
PD
1-PO
1 3Ru/MCM-41 0.5 230 140 62 20 38 13.0 Vanama
P.K.,
(2014)
2 5PtW/ZrSi 3 10 180 100 5 54.3 52 6.8 34.0 Zhu S.,
(2014) 3 Pt-STA/ZrO2 2 10 180 100 5 24.1 48.1 16.5 21.8 Zhu S.,
(2013)
4
Pt–STA/ZrO2
2 10 180 100 5
26.7 38.9 9.2 39.9
Zhu S.,
(2013)
Pt–LiSiW/ZrO2 43.5 53.6 14.2 24.1
Pt–KSiW/ZrO2 24 36.8 22 27.4
Pt–RbSiW/ZrO2 16.6 31.6 25.4 28.9
Pt–CsSiW/ZrO2 41.2 40.2 20.5 30.2
5
Pt–STA/ZrO2
4 10 200
100 5
99.7 0.9 5.1 80.0
Zhu S.,
(2012)
Pt–STA/ZrO2+1%
methanol
90.1 3.8 8.8 72.5
Pt–HPW/ZrO2 92.4 8.6 9.2 65.2
Pt–WO3/ZrO2 90.7 9.3 8.7 64.0
Pd–STA/ZrO2 25.3 10.9 49.2 27.4
Pt–STA/ZrO2 180 85.2 22.1 5.7
6 Pt-15STA/SiO2 4 10 200 100 6 81.2 38.7 20 28.0 Zhu S.,
(2012) 7 CuZnTi(2-2-1) 20 280 25 0.1 100 9 2 Feng Y. et
al., (2011) 8 3.0Pt/WZ10 2ml 60 130 10 4 70.2 45.6 2.6 44.2 Qin L. Z.,
(2010) 9 10Cu-15STA/SiO2 8 100 210 0.54 83.4 32.1 22.2 - Huang L.,
(2009)
181
Table A-3 Summary of Reported Catalysts and Reaction Conditions for Converting Glycerol into 1-propanol
Catalyst React.,
conten
t
Cat. loading,
wt%
Condition Conv Selectivity Reference
T,
oC
MPa Time,
h
1-PO 1,3P
D
1,2P
D 1 Raney Cu GL 2.5 18
0
initia
l 1
Mpa
6 12.4 50.5 5.5 Yue
C.J.(2014) Raney Cu/Al2O3 16.3 81 (1,2PP) 0 7.3
2 3Ru/MCM-41 GL 23
0
fix bed 62 13 20 38 P.K.
Vanama
(2014)
3 5Pt-Re/CNTs 17
0
4 8 55 26 15 52 Chenghao
Denga
(2014)
4 2.5PtW/ZrSi GL 3g 18
0
5 fix bed 41.5 35.3 46.3 9.8 Shanhui
Zhu (2014) 5 Ru(0.9)-Ir-
ReOx/SiO2
4 12
0
8 24 77.9 43.7 38.9 6 Masazumi
Tamura,
(2014)
6 5% Ru/HY GL 20
0
4 4 10.3 3.4 0 77.4 Jin S.
(2014) 5% Ru/HY-0.5H 17.9 2.9 78.5
7
5Pd–5Re/SBA-15 GL
4 20
0 8 18
40.7 24.6 8.2 59.9 Yuming Li
(2014) 5Pd/SBA-15 1.5 14.6 4.4 72.2
5Re/SBA-15 GL 3.1 38.7 6.7 49.6
5Pd–5Re/CNTs 49.6 30 8.2 52.5
8
Cu/boehmite GL
5 20
0 4 6
77.5 6.1 92.5 Z. Wu
(2013) Cu/γ-Al2O3 54.2 15.7 81.2
Cu/SiO2 GL 51.7 9.8 88.7
Ru/C 55.7 5.8 59.4
9 Pt/WOx/AlOOH GL BET SSA 123 100 18 37 2 Arundhathi
R., (2013) Pt/WOx/AlOOH BET SSA 56 100 32 37 1
10 Pt–STA/ZrO2 GL
18
0
5 fix bed 26.7 39.9 38.9 9.2 Zhu S.
(2013) Pt–CsSiW/ZrO2 41.2 30.2 40.2 20.5
11 Pt/Al2O3+STA GL 0.5mol% 20
0
4 18 49 30 28 7 Dam J.T.
(2013) Pt/SiO2+STA 10 73 10 5
182
12 Pt-H4SiW12O40/SiO2 GL 4g 20
0
5 In fix bed 88.5 36.9 27.2 24.8 Zhu
S.(2012) 13 PtAlOx/WO3 108.6 18
0
3 10 90 34 40 2 Mizugaki
T. (2012) Pt/WO3 GL 75 47 21 1
14 Pt/m-WO 25 18
0
5.5 12 18 33.8 39.3 4.1 Longjie L.
(2012) 15 NiSiO2 GL 8.5 g +
carborundum
32
0
6 In fix bed 99.9 42.8 0.6 4.6 Ryneveld
E. V.(2011) NiAlO3 96.1 35.5 2.2 1.8
16 Homogenous Ru
complex and
methane sulfonic
acid
GL 20
0
3.45 24 water–
sulfolane
18 yield Michelle E.
T. (2011) 17 Pt/WO3/TiO2/SiO2 18
0
5.5 15.3 25.1 50.5 9.2 Gong L.
(2010) Pt/WO3/TiO2 GL 7.5 28.2 43.7 11.7
18 Pt–Re/C 17
0
4 24 33 41 25 20 O.M.
Danie(2010
)
19 Ru–Re/SiO2-r200 GL 4 16
0
8 51 26.1 8.3 49.1 Ma
L.,(2010) 20 Rh–ReOx/SiO2
(Re/Rh = 0.5)
GL 4 12
0
8 5 79 35.3 13.8 38 Shinmi Y.
(2010) Rh–MoOx/SiO2
(Mo/Rh = 0.06)
12
0
8 5 44.1 49 5.6 30.4
21 Pt/WO3/ZrO2 GL 17
0
5.5 Ethanol 38.2 46.6 23 13.6 Leifeng G.
(2009) 22 Pt/WO3/ZrO2 GL
17
0
initia
l 5.5
Mpa
12 Ethanol 38.2 46.6 23 13.6 Leifeng
G.(2009) Ethanol-
water
45.7 32.1 21.2 8
23 Ru/Al2O3 GL 5 24
0
8 5 69 45 (1+2PrP) 0.7 37.9 Vasiliadou
E.S. (2009) 24 [Ru(OH2)3(4’-
phenyl-2,2’:6’,2’’-
terpy)](OTf)2 +
HOTf(4)
25
0
5.5 24 100 35 Taher
D.(2009) 25 Pt/WO3/ZrO2 GL 36.2 17
0
8 18 DMI 85.8 32.1 28.2 14.6 Kurosaka
T.(2008) Rh/WO3/ZrO2 86.4 26.3 5.4 32.6
26 Ru/C +Amberlyst GL
12
0
8 12.9 14.1 4.9 55.4 Miyazawa
T.(2006) 14
0
40.7 18.2 1 43.1
20
0
6.5 19.9 1.5 74.1
27 Rh_ReOx/SiO2
(Re/Rh=0.5)
GL 4 12
0
initia
l 8
24 100 76 3 Amada Y.
(2010) 1,2PD 4 12
0
8 48 water 98.2 68
GL 37.5 12
0
8 10 Water 29.3 41.3 5.4 22.6
183
28
Rh/SiO2 (G-6) +
Amberlyst
1,2PD 17.5 56.5
Furikado I.
(2007)
1,3PD 22.6 68.2
Ru/C+ Amberlyst
GL 38.8 28.9 0.8 28.8
1,2PD 6.3 28.2
1,3PD 77.7 32.8
29 Ir–ReOx/SiO2,
H2SO4, (H+/Re = 1),
Re:Ir=2
GL 4
12
0 8
12 58.6 40.7 44.8 5.4 Amada Y.
(2011) 1,2PD 2 46.9 87
1,3PD 2 10 93
30 Ir–ReOx/SiO2 (Re/Ir
= 1)., sulfuric, acid
(H+/Ir = 1)
GL 4
12
0 8 24
62.8 33 49 10 Nakagawa
Y.(2010) 1,2PD 71.7 85
1,3PD 22.6 >99
31
Pt–H4SiW12O40/ZrO2
Gl10%
4g 20
0 5 In fix bed
99.7 80 0.9 5.1
Zhu
S.(2012)
1,2PD 100 84.9
1,3PD 92.6 95.4
Ni–STA/ZrO2 Gl 24.7 16.1 5.7 52.6
Cu–STA/ZrO2 15.2 11.3 7.2 70.9
32
4.0Pt/WZ10 GL
2ml 13
0 4 24 In fix bed
84.5 66.5 26.4 0.7 Qin L.Z.
(2010) 2.0Pt/WZ10
41.6 44.2 44 3.6
1,2PD 78.3 90.7
1,3PD 22 99.9
33 Pt/SiO2–Al2O3
20%G
L
166 22
0
4.5 24 19 53.8(1+2Pr
P)
4.5 31.9 Gandarias I.
(2010)
24
0
87.6 59.7 0.7 11.2
1,2-
PDO
22
0
12.9 92.9(1+2PP
)
1,3-
PDO
22
0
10.5 98(1+2PP)
34 Rh–ReOx/SiO2
(Re/Rh = 0.5)
20%G
L
4 8 5 79 32.9 14 41.5
Rh–ReOx/SiO2
(Re/Rh = 0.5)
100% 15 16.3 28 51.2
184
Rh–ReOx/SiO2
(Re/Rh = 0.5)
20GL
%
12
0 2
38.4 26.7 16.1 46.9 Shimao A.
(2009) 1,2PD 14 81.7
1,3PD 11.8 97.9
35
Ru/Al2O3 GL,
4%
16
0
8 8 18 17.7 1.7 30.5 Yuming
Lia, (2014) Ru/Al2O3 +
1%Al/HZSM5(25)
30.5 19.1 1.6 20.9
Ru/Al2O3 1,2PD 3 2.3 11.9
1,3PD 3 5.8 16.8
36
Pt-HPW/ZrO2 Gl 2 18
0
5 12
25.5 37.9 32.9 10.9 Zhang
Y.(2013) Pt-STA/ZrO2 Gl 24.1 21.8 48.1 16.5
Pt-STA/ZrO2 1,2-
PDO
47.1 85.2
Pt-STA/ZrO2 1,3-
PDO
9.1 96.5
37
Ir-
ReOx/SiO2+H2SO4
GL20
%
4 12
0
8 24 61.1 36.6 43.2 9.2 Nakagawa
Y.(2012)
1,2-
PrD
4 38.9 89.7
1,3-
PrD
4 99.1
Ir-
ReOx/SiO2+Amberly
st 70 (50)
69.3 43.6 39 7
38 Ru/C + Amberlyst
GL 4+8%amberly
st
12
0 8 10
38.8 28.9 28.8 0.8 Miyazawa
T.(2006) 1,2PD 6.3 28.2
1,3PD 77.7 31
39
Rh/C + Amberlyst 20
4
14
0 8 10
64 53.2 7.2 19.5 Kusunoki
Y. (2005) Ru/C + Amberlyst
GL 12
0
12.9 14.1 4.9 55.4
1,2PD 3.5 55.8
1,3PD 12.8 27.7
40 Homogeneous Ru
complex catalyst
1,2PD 11
0
5.2 72 HBF4·Et2
O
85 10 Schlaf M.
(2009)
185
Appendix B GC Calibration Curve
Compound 1-PO 1-Butanol Ac. 1,2-PD EG 1,3PD 1,4-
Buta-diol Glycerol
Retention
Time (min) 2.129 2.788 4.57 9.165 10.09 15.61 22.35 32.23
Response
Factor 0.795 - 1.555 1.257 1.676 1.232 1.0 1.651
1-PO
Entry m1-PO,
mg
A1-PO mis, mg Ais A1-PO/Ais mac/mis y/x
1 33.7 3104.5 25 1949.78 1.59 1.35 0.847
2 60.1 5702.6 25 1968.70 2.90 2.40 0.829
3 101.7 10113.0 25 1946.54 5.20 4.07 0.783
4 152.4 15302.6 25 2000.65 7.65 6.11 0.799
5 202.2 19708.3 26 1956.05 9.82 7.78 0.792
Acetol
Entry mAc, mg AAc mis, mg Ais AAc/Ais mac/mis y/x
1 44.3 2173.5 25 1949.78 1.09 1.77 1.634
2 87.9 4455.7 25 1968.70 2.29 3.52 1.537
3 133.5 6765.1 25 1946.54 3.38 5.34 1.579
4 175.9 8740.5 25 2000.65 4.44 7.04 1.585
5 227.1 11921.3 25 1956.05 5.94 9.08 1.530
1,2-PD
Entry m1,2-PD,
mg
A1,2-PD mis, mg Ais A1,2-
PD/Ais
mac/mis y/x
1 56.1 3135.3 25 1949.78 1.61 2.24 1.395
2 107.2 6281.6 25 1968.70 3.19 4.30 1.346
3 155.7 9506.8 25 1946.54 4.88 6.22 1.273
4 204.6 12975.7 25 2000.65 6.49 8.18 1.262
186
5 303.7 19200.3 25 1956.05 9.82 12.15 1.238
6 602.1 38403.5 25 2005.18 19.15 24.08 1.258
EG
Entry mEG, mg AEG mis, mg Ais AEG/Ais mEG/mis y/x
1 33.0 1453.1 25 1949.78 0.75 1.32 1.771
2 51.8 2396.7 25 1968.70 1.22 2.07 1.702
3 86.1 3992.9 25 1946.54 2.05 3.44 1.679
4 125.9 5973.4 25 1956.05 3.03 5.04 1.664
1,3-PD
Entry m1,3-PD,
mg
A1,3-PD mis, mg Ais A1,3-
PD/Ais
m1,3-
PD/mis
y/x
1 28.6 1789.0 25 1949.78 0.92 1.14 1.247
2 53.2 3399.9 25 1968.70 1.73 2.13 1.232
3 79.6 5137.0 25 2000.65 2.57 3.18 1.240
4 103.7 6457.0 25 1946.54 3.32 4.15 1.250
5 155.5 10233.5 25 1956.05 5.09 6.22 1.222
Glycerol
Entry mGL,
mg
AGL mis, mg Ais AGL/Ais mGL/mis y/x
1 49.5 2195.7 25 2000.65 1.10 1.98 1.804
2 103.3 4611.2 25 1946.54 2.37 4.13 1.744
3 151.3 7012.5 25 1968.70 3.56 6.05 1.699
4 202.3 9293.1 25 1949.78 4.77 8.09 1.698
5 303.9 14513.7 25 1956.05 7.42 12.16 1.638
6 602.4 29275.7 25 1996.32 14.66 24.10 1.643
187
Figure B-1 Calibration Curve for Propanol
Figure B-2 Calibration Curve for Acetol.
188
Figure B-3 Calibration Curve for 1,2-PD
Figure B-4 Calibration Curve for EG.
189
Figure B-5 Calibration Curve for 13PD.
Figure B-6 Calibration Curve for Glycerol.
190
Identification of products by GC
Figure B-7 A typical Chromatogram of a GC Calibration Standard
Figure B-8 Chromatogram of a GC products using 10Ni/30HSiW/Al2O3 calcinated at 450oC
191
Appendix C Acid concentration calculation (mmol/gcat)
The TPD data was deconvoluted into 3 peaks (namely weak, medium and strong acid sites) using
a Gaussian fitting method. Lower temperature desorption corresponds to weak acid sites and
higher tempereture to medium, strong acid sites. The number of moles of NH3 desorbed during
desorption step can be calculated using Equation C-1 and Equation C-2.
100*)__(
)__(*)_(_
areaoncalibaratimean
gasanalyticalpercentvolumeloopValuenCalibratio C-1
5.24*)_(
)_(*)_()/(
weightsample
valuencalibratioareaanalyticalgcatmmolUptake C-2
Calculation NH3 desorbed using catalyst of 1Ni30HSiW/Al2O3
Sample weight: 0.123g
Loop volume: 0.524ml
Percent analytical gas 5.16%
Analytical area: Weak acid site (167oC): 18464; Medium acid site (259oC): 24998; Strong acid site
(460oC): 26702
Weak acid site: 0.228 mmol/gcat. Medium acid site 0.308 mmol/gcat. Strong acid site: 0.330
mmol/gcat
Total acidity: 0.228 + 0.308 + 0.330 = 0.866 mmol/gcat
Calculation for Table 4-1
Pulse HSiW/Al 1Ni 1Pd 1Pt 10Ni 10Cu
1 679.34 726.83 709.41 678.09 658.09 687.26
2 722.35 712.06 733.96 739.37 650.99 692.84
3 721.08 697.22 670.72 710.22 716.37 687.25
4 734.46 680.82 681.88 714 694.44 649.37
5 802.38 720.28 700.18 708.81 691.67 645.05
Mean area 731.92 707.44 699.23 710.10 682.31 672.35
Loop volume
(mL)
0.524 0.524 0.524 0.524 0.524 0.524
Sample
weight (g)
0.123 0.123 0.120 0.122 0.120 0.120
Calibration
value
3.6E-05 3.7E-05 3.7E-05 3.7E-05 3.8E-05 3.9E-05
Total acid
amount
mmol/g
0.989
0.866
0.873
0.869
0.572
0.657
192
The TPD curves are deconvoluted into 3 peaks using a Gaussian curve-fitting
193
Catalyst
Weak acid site
mmol/g
/(Temp.)
Medium acid
site mmol/g
/(Temp.)
Strong acid
site mmol/g
/(Temp.)
Total acid
amount,
mmol/g
30HSiW/Al2O3 0.149/ (155oC) 0.379/ (243oC) 0.461/ (439oC) 0.989
1Ni//30HSiW/Al2O3 0.228/ (167oC) 0.308/ (259oC) 0.330/ (460oC) 0.866
1Pd/30HSiW/Al2O3 0.205/ (172oC) 0.242/ (254oC) 0.425/ (442oC) 0.873
1Pt/30HSiW/Al2O3 0.235/ (178oC) 0.194/ (281oC) 0.441/ (428oC) 0.869
10Ni/30HSiW/Al2O3 0.124/ (162oC) 0.233/ (246oC) 0.215/ (427oC) 0.572
10Cu/30HSiW/Al2O3 0.108/ (162oC) 0.201/ (230oC) 0.347/ (345oC) 0.657
194
Appendix D Glycerol conversion, product selectivity
and rate constant calculations
remainglycerolofmoleproductbasedcarbonallofmole
productbasedcarbonallofmoleconversionglycerol
________
______
D-1
productbasedcarbonallofmole
POofmoleyselectivitPO
_____
_1____1 D-2
productbasedcarbonallofmole
PDofmoleyselectivitPD
_____
_13____13 D-3
%100*___
__________
glycerolinitialofmole
remainglycerolofmoleproductbasedcarbonallofmolebalancemassGlycerol
D-4
Calculation for Table 5-6 “Effect of temperature on the conversion of glycerol and the distribution
to products in the hydrogenolysis of glycerol”
Experimental Conditions:
Temperature: 240ºC; Initial Hydrogen Pressure: 580PSI; Stirring Speed: 700RPM
Catalyst: 10Ni/30HSiW/Al2O3: prepared by incipient wetness impregnation
Reactant Feed: 30g glycerol, 70g water, 2g catalyst
Table D-1. GC data
Compound Retention time Area
1-PO 2.129 7050.218
Acetol 4.57 27.455
1,2-PD 9.165 106.253
EG 10.095 0
1,3-PD 15.608 0
Glycerol 23.25 2752.582
I.S. 22.35 1782.696
Others 289.115
Table D-2. Response Factor for Each Compound
195
1-PO Acetol 1,2-PD EG 1,3-PD Glycerol Others
MW 60.1 74.08 76.09 62.07 76.09 92.09 73.52
RF 0.795 1.555 1.257 1.676 1.232 1.651 1.361
Mass of GC sample: 131mg
Solvent: 1ml of 1-butanol and 5mg of 1,4-butanediol (I.S.) mixture (5mg of I.S.)
mgA
Akmpropanolm
SI
PPSI 72.15
7.1782
212.7050795.05)(
..
..
mmolmgmmol
mg
propanolMW
propanolmpropanoln 2616.0
/1.60
72.15
)(
)()(
mgA
Akmacetolm
SI
AASI 1197.0
7.1782
456.27555.15)(
..
..
mmolmgmmol
mg
acetolMW
acetolmacetoln 0016.0
/1.74
19.0
)(
)()(
mgA
AkmPDm
SI
PDPDSI 375.0
7.1782
25.106257.15)12(
..
1212..
mmolmgmmol
mg
PDMW
PDmPDn 0049.0
/1.76
447.0
)12(
)12()12(
mgA
AkmGLm
SI
GL
GLSI 75.127.1782
6.2752651.15)(
..
..
mmolmgmmol
mg
GLMW
GLmGLn 138.0
/1.92
75.12
)(
)()(
mgA
Akmunknownm
SI
unknown
unknownsSI 104.17.1782
12.289346.15)(
..
..
mmolmgmmol
mg
unknownMW
unknownmunknownn 015.0
/52.73
104.1
)(
)()(
196
mmol
unknownnPDnEGnPDnAcetolnnPOnnproductsn product
2831.0015.000.0000.00049.00016.02616.0
)()13()()12()()()(
%4.67%100*)138.02831.0
2831.0(%100)(
GLproducts
products
GLnn
nConversion
%4.92%100*)2831.0
2616.0(%100)(
products
nPO
POnn
nySelectivit
%3.62%100*)138.02831.0
2616.0(%100)(
GLproducts
nPO
nPOnn
nYield
%7.1%100*)2831.0
0049.0(%100)( 12
12 products
PDPD
n
nySelectivit
%2.1%100*)138.02831.0
0049.0(%100)( 12
12
GLproducts
PDPD
nn
nYield
%7.98%100*30131.0
1.92*)138.02831.0(%100*
30
*)(
__
Sample
GLGLproducts
m
MWnn
balancemassGlycerol
Calculation of the reaction rate for the hydrogenolysis of glycerol to 1-PO (Table 5-7 for 240oC)
A sample calculation of the kinetic determination of glycerol hydrogenolysis using an integral
method was performed under the following condition: Temperature of 240ºC; initial Hydrogen
Pressure of 580PSI; Stirring Speed - 700RPM; 30g glycerol, 70g water, 2g catalyst). The samples
taken from the reaction mixture after 0.5, 1, 2, 3, 4, 5 and 7 hours were analyzed by GC.
Experimental data for this reaction are listed in Table D-3; they are provided as [GL], ln[GL]
versus time. A plot of ln[GL] vs. time in Figure D2 has the form of a straight line, hydrogen was
supplied continuously for the whole reaction thus it is suggested that the reaction is first-order in
Gl and a pseudo-first-order kinetics has been used to calculate the rate constant of reaction. The
plot of ln[GL] vs. time is represented by the equation D-5.
Table D-3. Concentration of glycerol as a function of time using the 10Ni30HSiW/Al2O3 catalyst
Time, h 0 0.5 1 2 3 4 5 7
[GL], mol/l 3.47 3.27 2.97 2.17 1.71 1.46 1.30 1.04
ln[GL] 1.24 1.19 1.09 0.78 0.54 0.38 0.26 0.04
197
−𝒅[𝑮𝑳]
𝒅𝒕= 𝒌𝒐𝒃𝒔 ∗ [𝑮𝑳] => 𝑳𝒏[𝑮𝑳] = −𝒌𝒐𝒃𝒔 ∗ 𝒕 + 𝑳𝒏[𝑮𝑳𝒕=𝟎] D-5
Figure D-1 Conversion as a time function
Figure D-2 Pseudo-first order kinetic plot
The plot of ln[GL] vs. time is represented by the following equation:
y = -4.77E-05x + 1.19E+00
From the kinetic plot it is suggested that the rate constant is kobs=4.77E-05 s-1.
198
Appendix E Data of hydrogenolysis of Glycerol (some
typical experiments)
E1. Effect of metals on the hydrogenolysis of glycerol using Stainless
Steel batch reactor
Experiment #1
30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol, 70g of
DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1 1.6 0.0 0.0 5.5 0.0 9.5 85.0
2 4.8 0.0 0.0 4.9 0.0 13.1 82.0
3 6.7 0.0 0.0 6.5 0.0 14.3 79.2
4 10.3 0.0 0.0 5.7 0.0 18.6 75.7
6 13.2 0.0 0.0 6.1 0.0 23.7 70.2
8 14.5 0.0 0.0 6.0 0.0 30.5 63.5
Experiment #2
1Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1 6.7 0.0 8.1 15.5 0.0 37.2 39.2
2 9.6 0.0 7.6 12.8 0.0 46.0 33.6
3 17.6 0.0 7.2 6.9 0.0 50.0 36.0
4 20.6 0.0 9.0 6.5 0.0 53.2 31.3
6 29.9 3.9 5.5 4.5 0.0 51.2 35.0
8 39.2 3.0 4.1 3.3 0.0 54.7 34.9
Experiment #2
1Pd/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1 6.4 0.0 9.7 15.3 0.0 29.5 45.5
2 12.9 0.0 7.7 10.4 0.0 36.2 45.6
199
3 17.5 0.0 6.0 6.1 0.0 43.5 44.4
4 22.3 0.0 5.0 4.6 0.0 48.0 42.3
6 29.0 4.2 3.8 3.7 0.0 44.9 43.4
8 34.1 5.4 4.7 4.1 0.0 51.4 34.5
Experiment #4
1Pt/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1 7.8 0.0 17.9 15.5 0.0 56.8 9.7
2 13.5 9.3 15.5 8.5 0.0 57.8 8.9
3 19.1 10.3 12.0 4.6 0.0 56.1 17.0
4 25.5 11.5 10.1 4.2 0.0 57.4 16.8
6 36.0 11.0 7.1 3.0 0.0 58.2 20.7
8 45.3 10.5 5.7 2.5 1.8 59.2 20.3
Experiment #5
10Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 10.7 0.0 13.5 12.0 0.0 55.2 19.4
2.3 16.0 10.0 13.5 5.8 4.9 52.4 13.3
4.0 18.5 4.9 9.4 5.3 0.0 47.7 32.8
6.0 29.3 4.5 8.9 4.8 2.7 51.3 27.8
8.0 33.2 7.9 10.5 3.8 4.4 60.3 12.7
Experiment #6
10Cu/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 880PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 4g catalyst, t = 8 hours
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 1.1 0.0 0.0 4.4 0.0 10.6 85.0
2.0 5.7 0.0 0.0 6.0 0.0 12.2 81.9
3.0 8.0 0.0 2.5 5.8 0.0 15.4 76.2
4.0 11.4 0.0 3.6 4.6 0.0 17.6 74.2
6.0 14.7 0.0 3.8 8.0 0.0 26.4 61.8
8.0 18.4 0.0 4.2 5.3 0.0 31.8 58.7
200
E2. Effect of calcination temperature on the hydrogenolysis of
glycerol using a Hasteylloy reactor
Experiment #1
10Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 580PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 2g catalyst, t = 7 hours, calcination temperature = 350oC
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 21.5 0.0 0.0 3.1 0.0 81.6 15.3
2.0 43.3 0.0 0.0 1.6 0.0 87.6 10.8
3.0 57.8 0.0 0.0 1.0 0.0 89.5 9.5
4.0 67.4 0.0 0.0 0.7 0.0 90.1 9.3
5.0 77.1 0.0 0.0 0.5 0.0 91.3 8.2
7.0 86.5 0.0 0.0 0.4 0.0 91.7 7.9
Experiment #2
10Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 580PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 2g catalyst, t = 7 hours, calcination temperature = 450oC
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 21.9 0.0 0.0 2.9 0.0 77.7 19.4
2.0 44.4 0.0 0.0 1.4 0.0 85.0 13.5
3.0 62.7 0.0 0.0 0.9 0.0 89.7 9.4
4.0 69.8 0.0 0.0 0.7 0.0 90.5 8.8
5.0 82.3 0.0 0.0 0.4 0.0 90.6 9.1
7.0 90.1 0.0 0.0 0.3 0.0 92.9 6.8
Experiment #3
10Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 580PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 2g catalyst, t = 7 hours, calcination temperature = 550oC
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 7.4 0.0 0.0 7.7 0.0 49.7 42.6
2.0 13.1 0.0 0.0 5.9 0.0 58.7 35.4
3.0 21.1 0.0 0.0 4.1 0.0 65.8 30.1
4.0 30.2 0.0 3.0 3.1 0.0 66.8 27.1
5.0 41.0 0.0 2.9 2.1 0.0 69.5 25.6
7.0 46.2 0.0 2.9 1.7 0.0 71.5 23.9
201
Experiment #4
10Ni/30HSiW/Al2O3 catalyst, T = 240oC, PH2 = 580PSI, SR = 700 rpm, 30g of glycerol,
70g of DI water, 2g catalyst, t = 7 hours, calcination temperature = 650oC
Time
(h)
Conv
(mol%)
Selectivity (mol%)
1,3PD 12PD Act EG 1-PO Others
1.0 3.1 0.0 0.0 0.0 0.0 60.7 39.3
2.0 5.3 0.0 0.0 10.7 0.0 60.5 28.8
3.0 8.6 0.0 0.0 8.6 0.0 62.4 29.0
4.0 10.3 0.0 0.0 7.4 0.0 64.4 28.3
5.0 12.7 0.0 0.0 5.7 0.0 65.6 28.7
7.0 21.3 0.0 0.0 4.4 0.0 64.9 30.7
202
Appendix F Permission to Re-print Copyrighted
Material
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